Unit 4 Learning Objectives(Chapters 12-16) Flashcards
1
Q
Describe the major functions of the nervous system.
A
Employs electrical and chemical means to send messages from cell to cell
In combination with the endocrine system, it maintains internal coordination.
-Receives information about changes in the body and external environment
-Processes this information, relates it to past experiences, and determines appropriate response
-Issues commands to muscles and glands cells to carry out such a response
2
Q
Describe the basic pathway of the nervous system in order from beginning to end
A
1) Sensory receptor detects a stimulus
2) Sensory (afferent) neuron
3) Integrating center: central nervous system
4) Motor (efferent) neuron
5) Effector: responds (muscle or gland)
3
Q
List the parts of the nervous system that constitute the CNS and those that constitute the PNS.
A
- CNS: brain and spinal cord (enclosed by meninges, the cranium, and vertebrae)
- PNS: rest of the nervous system except the brain and spinal cord; composed of nerves & ganglia
4
Q
Differentiate between the somatic and autonomic divisions of the nervous system.
A
1) Somatic (voluntary) nervous system:
- Motor neurons to skeletal muscle tissue
- Only 1 motor neuron is used
- Somatic reflexes: involuntary muscle contractions
2) Autonomic (involuntary) nervous system”
- Motor neurons to smooth & cardiac muscle, endocrine glands, & exocrine glands
- 2 motor neurons used
- Autonomic/visceral reflexes; involuntary responses
5
Q
Differentiate between the sympathetic and the parasympathetic divisions of the autonomic nervous system.
A
1) Sympathetic division: Tends to arouse body for action
- Motor neurons originate from thoracolumbar region
- “Fight or flight” responses; “E” responses (excitement, emergency, exercise)
2) Parasympathetic division: Tends to have calming effect
- Motor neurons originate from craniosacral region
- “Resting and digesting” responses; SLUDD (salivation, lacrimation, urination, digestion, defecation)
6
Q
Describe three functional properties found in all neurons.
A
1) Excitability (irritability)
Respond to environmental changes called stimuli; produce an electrical signal
2) Conductivity
Conduct the electrical signal to other cells
3) Secretion
When an electrical signal reaches the end of nerve fiber, the cell secretes a chemical neurotransmitter that influences the next cell
7
Q
Define the three basic functional categories of neurons.
A
1) Sensory (afferent) neurons
Detect stimuli & transmit information toward CNS
2) Interneurons (association neurons)
Lie entirely within CNS; connects motor and sensory pathways
Makes decisions (integrating center)
About 90% of all neurons
3) Motor (efferent) neuron
Send signals out to muscles and gland cells (the effectors)
8
Q
Identify the parts of a neuron including soma (cell body), axon, and dendrites.
A
1) Soma: control center of neuron
Also called neurosoma or cell body, it has a nucleus with one nucleolus
Cytoplasm contains mitochondria, lysosomes, Golgi complex, inclusions, extensive rough ER and cytoskeleton.
Inclusions include things like glycogen, lipid droplets, melanin, and lipofuscin pigment (produced when lysosomes digest old organelles)
Cytoskeleton has dense mesh of microtubules and neurofibrils (bundles of actin filaments) that compartmentalizes rough ER into dark-staining Nissl bodies
No centrioles, no mitosis. However, extreme longevity.
2) Dendrites: branches that come off the soma
Receives signals from other neurons; the more dendrites the neuron has, the more information it can receive
3) Axon (nerve fiber)
Originates from axon hillock and transmits signals away from soma
Only one (or none) per neuron
Mostly unbranched except for axon collaterals
Axolemma may be enclosed by myelin sheath
9
Q
Describe multipolar, bipolar, unipolar, and anaoxic neurons
A
1) Multipolar neuron
One axon and multiple dendrites
Most common type; makes up most neurons in the CNS
2) Bipolar neuron
Has one axon and one dendrite
3) Unipolar neuron
Has one single process leading away from soma
Sensory cells from skin and organs to spinal cord (somas in dorsal root ganglia)
4) Anaxonic neuron
Has many dendrites but no axon
10
Q
The most common type of neuron shape is what?
A
Multipolar
11
Q
Define the terms ganglion, nerve, tract, and synapse.
A
1) Ganglion: a knot-like swelling in a nerve where neuron cell bodies are concentrated; found in the PNS.
2) Nerve: bundle of nerve fibers (axons) wrapped in fibrous connective tissue; spinal versus cranial nerves. Found in the PNS.
3) Tract: The CNS equivalent of a nerve; it is a bundle of axons, which are often myelinated.
4) Synapse: The junction between two neurons, or between a neuron and muscle tissue.
12
Q
Explain how neurons transport materials between the cell body and the tips of the axon.
A
- Proteins made in soma need to be transported to axon & axon terminal to repair axolemma and to transport organelles; they do this via a two-way passage: anterograde (away from soma) and retrograde (toward soma)
- These two types of transport use microtubules (to guide materials along axon) and motor proteins (kinesin and dynein) that carry materials “on their backs” while they “crawl” along microtubules.
13
Q
Name and describe the 4 types of cells in the CNS that aid neurons
A
1) Oligodendrocytes
Form myelin sheaths in CNS that speed signal conduction using arm-like processes
2) Ependymal cells
Line internal cavities of the brain; secrete and circulate cerebrospinal fluid (CSF)
3) Microglia
Wander through CNS looking for debris and damage, and get rid of it via phagocytosis.
4) Astrocytes
Most abundant glial cell in CNS; covers brain surface and most nonsynaptic regions of neurons in the gray matter (framework)
Forms blood-brain barrier using perivascular feet
Absorbs excess neurotransmitters and ions
Astrocytosis or sclerosis; when neuron is damaged, astrocytes form hardened scar tissue and fill in space
14
Q
Name and describe the 2 types of cells in the PNS that aid neurons
A
1) Schwann cells
Produce a myelin sheath around axons similar to the ones produced by oligodendrocytes in CNS
Also assist in regeneration of damaged fibers
2) Satellite cells
Surround the somas in ganglia of the PNS
Provide electrical insulation around the soma
Regulate the chemical environment of the neurons
Similar in function to astrocytes.
15
Q
Describe the myelin sheath that is found around certain nerve fibers, and explain its importance.
A
- Serves as insulation around a nerve fiber (axon)
- Formed by oligodendrocytes in CNS and Schwann cells in PNS
- Consists of the plasma membrane of glial cells
- 20% protein and 80% lipid
- MUCH faster than unmyelinated axons, which is why it’s so critical.
16
Q
Discuss the 3 cell types from which brain tumors typically originate.
A
- Meninges (protective membranes of CNS)
- Metastasis from other tumors in other organs
- Glial cells (mitotically active throughout life)
17
Q
Describe gliomas and discuss whether or not neurons are a major source of tumors
A
1) Gliomas: grow rapidly and are highly malignant
Blood–brain barrier decreases effectiveness of chemotherapy
Treatment consists of radiation or surgery
2) Mature neurons undergo very little mitosis, so not typically a cause of tumors
18
Q
Describe the problems with the degenerative disorder Multiple Sclerosis
A
- A degenerative disorder of the myelin sheath; oligodendrocytes and myelin sheaths in the CNS deteriorate
- Myelin is replaced by hardened scar tissue
- Nerve conduction disrupted (double vision, tremors, numbness, speech defects)
- Onset between 20 and 40 years
- Cause may be autoimmune triggered by virus
19
Q
Describe the problems with the degenerative disorder Tay-Sachs disease.
A
- A hereditary disorder of infants of Eastern European Jewish ancestry
- Abnormal accumulation of glycolipid called GM2 (ganglioside) in the myelin sheath disrupts conduction of nerve signals
- Caused by dysfunctional lysosomes
- Symptoms include blindness, loss of coordination, and dementia
- Fatal before age 4
20
Q
Explain how certain damaged nerve fibers regenerate, and what regeneration requires
A
1) Steps of regeneration:
- Fiber distal to the injury degenerates
- Axon stump sprouts multiple growth processes
- Schwann cells, basal lamina and neurilemma form a regeneration tube
2) Only peripheral nerve fibers can regenerate and only if:
- the soma is intact
- some neurilemma remains
21
Q
Describe what 2 factors will increase the conduction speed of nerve fibers.
A
1) Diameter of fiber
Larger fibers have more surface area and conduct signals more rapidly
2) Presence or absence of myelin
Myelin further speeds signal conduction
22
Q
Explain why a cell has an electrical charge difference (voltage) across its membrane.
A
It’s the result of 3 combined factors:
1) Ions diffuse down their concentration gradient through the membrane
2) Plasma membrane is selectively permeable and allows some ions to pass easier than others
3) Electrical attraction of cations and anions to each other
23
Q
Explain how ion channels affect neuron selective permeability.
A
〖𝐍𝐚〗^+/𝐊^+ pump moves 3 Na^+ out for every 2 K^+ it brings in. This exchange of 3 positive charges for only 2 positive charges contributes about −3 mV to the cell’s resting membrane potential of −70 mV. It works continuously to compensate for Na+ and K+ leakage.
24
Q
Contrast the relative concentrations of sodium and potassium ions inside & outside of a cell.
A
Na+ is more concentrated outside of the cell (ECF) K+ is more concentrated inside the cell (ICF).
25
Describe the characteristics of local potentials, and explain how stimulation of a neuron causes a local electrical response in its membrane.
1) Local (graded) potentials are defined as changes in membrane potential of a neuron occurring at & nearby the part of the cell that is stimulated
- Short distances; die out quickly
- On dendrites and cell bodies
2) Sodium gates open in response to chemicals, light, heat or mechanical stimulation
- Size of signal depends on stimulus strength
- This leads to the membrane doing one of two things:
depolarize: leads to an action potential or
hyperpolarize: prevents an action potential
26
Describe the three changes in membrane potentials (depolarization, repolarization, hyperpolarization) that can occur.
1) Depolarization: the inside of the membrane becomes less negative. Will reverse polarity. Can lead to an electrical impulse.
2) Repolarization: the membrane returns to its resting membrane potential
3) Hyperpolarization: the inside of the membrane becomes more negative than the resting potential; inhibits an electrical impulse.
27
Compare and contrast the properties and location of local potentials and action potentials.
- Action potentials follow an all-or-none law; if threshold is reached, neuron fires at its maximum voltage. If threshold is not reached, it does not fire. This is not a property of local potentials.
- Action potentials do not get weaker with distance, whereas local potentials do
- Action potentials are irreversible; once started, it goes to completion and cannot be stopped. However, local potentials are not irreversible.
28
Discuss the sequence of events that must occur for an action potential to be generated.
- Arrival of current at axon hillock depolarizes membrane
| - Depolarization must reach threshold: critical voltage (about -55 mV) required to open voltage-regulated gates
29
Define threshold and refractory period.
1) Refractory period: the period of resistance to stimulation.
2) Threshold: the critical voltage (about -55 mV) required to open voltage-regulated gates
30
Explain how different intensities of sensations can occur.
All nerve action potentials are identical in strength, so different intensities of sensations result from:
1) the frequency of the stimulus
2) the number of neurons stimulated
31
Explain the two ways (continuous and saltatory) a nerve signal is conducted down an axon.
1) Saltatory conduction:
- Myelinated fibers conduct signals with saltatory conduction; the signal seems to jump from node of Ranvier to node of Ranvier
- Very fast
2) Continuous conduction:
- Unmyelinated fibers have voltage-gated channels along their entire length
- Produce action potential the entire length of the axon
- Chain reaction continues until the nerve signal reaches the end of the axon; the nerve signal is like a wave of falling dominos.
- The refractory membrane ensures that the action potential travels in one direction
32
List the structures that comprise a chemical synapse
Presynaptic neurons have synaptic vesicles with neurotransmitter and postsynaptic have receptors and ligand-regulated ion channels
33
List the sequence of events at the chemical synapse.
1) Nerve impulses reach the axonal terminal of presynaptic neuron and open Ca2+ channels
2) Neurotransmitter is released from synaptic vesicle into synaptic cleft via exocytosis (because of the Ca2+)
3) Neurotransmitter crosses synaptic cleft and binds to receptors on postsynaptic neuron
4) Postsynaptic membrane permeability changes, causing an excitatory (EPSP) or inhibitory (IPSP) effect
34
Compare and contrast chemical and electrical synapses.
1) Electrical:
- Spreads through gap junctions
- Faster
- Two-way transmission
- Can’t make decisions
2) Chemical:
- One-way transmission
- From a presynaptic neuron to a postsynaptic neuron; does not use gap junctions.
- Uses neurotransmitters
- Can make decisions.
- Slower than electrical synapses.
35
Contrast an excitatory postsynaptic potential (EPSP) with an inhibitory postsynaptic potential (IPSP).
EPSPs depolarize the cell, whereas IPSPs hyperpolarize the cell.
36
Discuss the relationship between a neurotransmitter and its receptor.
The same neurotransmitter can have completely different effects on different receptors; the postsynaptic membrane permeability will change, but it can cause either an excitatory (EPSP) or inhibitory (IPSP) effect depending on the receptor’s postsynaptic potential.
37
Describe the events of cholinergic synaptic transmission in proper chronological order.
1) Nerve impulses reach the axonal terminal of presynaptic neuron and open Ca2+ channels
2) ACh (the neurotransmitter) is released into synaptic cleft via exocytosis
3) ACh crosses synaptic cleft and binds to receptors on postsynaptic neuron
4) Postsynaptic membrane permeability changes, causing an excitatory (EPSP) or inhibitory (IPSP) effect
38
List the six chemical categories of neurotransmitters.
1) Acetylcholine
2) Amino acids
3) Monoamines
4) Purines
5) Neuropeptides
6) Gasses.
39
Explain the 3 ways in which the stimulation of a postsynaptic cell can be stopped
1) Diffusion
move down concentration gradient away from synapse
2) Enzymatic degradation
Ex: acetylcholinesterase and monoamine oxidase
3) Uptake by neurons or glia cells
neurotransmitter transporters
40
Explain how a neuron “decides” whether or not to generate action potentials.
The balance between EPSPs and IPSPs using summation enables the nervous system to make decisions
41
Differentiate between temporal summation and spatial summation.
1) Temporal summation: occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades
2) Spatial summation: occurs when EPSPs from several different synapses add up to threshold at an axon hillock
- An example of facilitation; a process in which one neuron enhances the effect of another
42
Describe the problems and treatments of the degenerative disorder of Alzheimer Disease.
1) Problems:
- It’s the 6th leading cause of death in United States
- Symptoms include memory loss for recent events, moody, combative, lose ability to talk, walk, and eat
- Show deficiencies of acetylcholine
- Diagnosis confirmed at autopsy
- Atrophy of gyri (folds) and formation of abnormal proteins
- Blocks normal synaptic function
2) Treatment:
- Trying to find ways to clear or halt the production of abnormal proteins
- No prevention or cure: SHIELD (sleep, handle stress, interact with others, exercise, learn new things, diet (mind diet)
43
State the four principal functions of the spinal cord.
1) Conduction: nerve fibers conduct information up (ascending) & down (descending) spinal cord; white matter
2) Neural integration: neurons receive input from sources, integrates it, and decides appropriate output (e.g., bladder control) – white or gray matter?
3) Locomotion: groups of neurons that coordinate repetitive sequences of contractions for walking
4) Reflexes: involuntary responses to stimuli
44
Describe the gross anatomy of the spinal cord and spinal nerves.
- Spinal cord is shaped like a flattened cylinder
- Arises from the brainstem
- Extends from foramen magnum to L1-L2
- Growth of cord stops at approximately age 5
- Gives rise to 31 pairs of spinal nerves
45
Describe the meninges, from superficial to deep, that enclose the brain and spinal cord.
1) Dura mater: most superficial
2) Arachnoid mater: middle
3) Pia mater: most deep
- Subarachnoid space is located between arachnoid and pia mater; circulates CSF.
- Epidural space is the space above the dura mater
46
Contrast the relative position of gray matter and white matter in the spinal cord compared to the white and gray matter in the brain.
The relationship between white and gray matter in the brain and spinal cord is inverse:
- In the brain, the cortical white matter is deep to gray matter
- In the spinal cord, gray matter is deep to white matter.
47
Trace the ascending pathway followed by nerve signals traveling up and down the spinal cord, and describe the functions of the neurons involved
- Ascending tracts carry sensory signals up the spinal cord
- Uses three neurons from origin (receptors) to destinations in the sensory areas of the brain
1) First neuron: detect stimulus and transmit signal to spinal cord or brainstem (Receptor to spinal cord or brainstem)
2) Second neuron: from spinal cord/brainstem continues to the thalamus (Spinal cord or brainstem to thalamus)
3) Third neuron: carries the signal the rest of the way to the sensory region of the cerebral cortex (Thalamus to cortex).
48
Trace the descending pathway followed by nerve signals traveling up and down the spinal cord
- Descending tracts: carry motor signals down brainstem and spinal cord
- Involve two motor neurons called upper and lower motor neurons
- Decussation of somatic neurons cross in Medulla oblongata
49
List the definitions of ascending versus descending tracts, decussation, and contralateral versus ipsilateral.
- Ascending: carry sensory information up
- Descending: carry motor information down
- Decussation: crossing midline so that brain senses and controls contralateral side of body
- Contralateral: when the origin and destination on opposite sides of the body
- Ipsilateral: when the origin and destination on the same side of the body; does not decussate
50
Explain how decussation occurs in sensory and motor pathways and predict how decussation impacts the correlation of brain damage.
- Decussation means that the sensory and motor tracts cross from one side of the brain as they travel from the top to bottom (and vice versa).
- This is why, for example, if you damage the right side of your brain you may have trouble coordinating/moving the (contralateral) left side of your body.
51
Describe the effects of Polio, which destroys somatic motor neurons.
- Caused by the poliovirus (spreads by fecal contamination of water)
- Destroys motor neurons in brainstem and anterior horn of spinal cord
- Signs of polio include muscle pain, weakness, and loss of some reflexes
- Followed by paralysis, muscular atrophy, and -respiratory arrest
52
What two diseases discussed in class destroy somatic motor neurons?
Polio and ALS
53
Describe the effects of ALS, which destroys somatic motor neurons.
- Known as Amyotrophic lateral sclerosis (ALS) or Lou Gehrig disease
- Destruction of motor neurons and muscular atrophy
- Sclerosis (scarring) of lateral regions of the spinal cord
- Astrocytes fail to reabsorb the neurotransmitter glutamate from the tissue fluid; accumulates to toxic levels
- Early signs: muscular weakness; difficulty speaking, swallowing, and using hands
- Sensory & intellectual functions remain unaffected
54
Describe the anatomy of nerves and ganglia
Ganglia: a cluster of neurosomas outside the CNS enveloped in an endoneurium (continuous with nerve)
Nerves: a cord-like organ composed of numerous nerve fibers (axons) bound together by connective tissue
55
Discuss how the structures root, nerve, ramus, plexus, tract and ganglion relate to one another
Ganglia are continuous with a nerve, and found near both the posterior (dorsal) and anterior (ventral) roots of spinal nerves; they’re called posterior root ganglion and anterior root ganglion.
A nerve is a bundle of axons found in the peripheral nervous system, and a bundle of axons found within the central nervous system are called tracts.
The portion of the nerve outside the vertebra divides into rami (singular ramus) distal branches.
In any other region besides the thoracic region of the spine, the anterior rami of nerves give rise to plexuses.
56
Describe the differences between the anterior and posterior roots of the spine
Anterior (ventral) root: contains motor neurons.
| Posterior (dorsal) root: contains sensory neurons.
57
Describe where the 31 pairs of spinal nerves are located
```
8 cervical (C1–C8)
(First cervical nerve exits between skull and atlas, others exit at intervertebral foramina)
12 thoracic (T1–T12)
5 lumbar (L1–L5)
5 sacral (S1–S5)
1 coccygeal (Co1)
```
58
What nerve(s) does the cervical plexus contain?
Phrenic nerve
59
What nerve(s) does the brachial plexus contain?
Axillary nerve, radial nerve, median nerve, and ulnar nerve
60
What nerve(s) does the lumbar plexus contain?
Femoral and obturator nerves
61
What nerve(s) does the sacral plexus contain?
Sciatic and pudendal nerves
62
Define reflex and explain how reflexes differ from other motor actions.
- Reflexes: defined as quick, involuntary, stereotyped reactions of glands or muscle to stimulation
- Unique characteristics of reflexes:
1) Reflexes require stimulation: not spontaneous actions, but responses to sensory input
2) Reflexes are quick: involve few, if any, interneurons and minimum synaptic delay
3) Reflexes are involuntary: occur without intent and are difficult to suppress
4) Reflexes are stereotyped: occur essentially the same way every time
63
Describe the general components of a typical somatic reflex arc.
```
Somatic receptors: In skin, muscles, or tendons
Afferent (sensory) nerve fiber
Integrating center
Efferent (motor) nerve fiber
Effectors: skeletal muscles
```
64
Give an example of a stretch reflex
The knee-jerk (patellar) monosynaptic reflex.
65
List the major subdivisions of the brain
```
Cerebrum
Cerebellum
Brainstem
Midbrain, pons, medulla oblongata
Diencephalon
Hypothalamus, Thalamus, & Epithalamus
```
66
Differentiate between rostral and caudal
Rostral: toward the forehead
Caudal: toward the spinal cord
67
Describe the locations of the brain’s gray and white matter.
-Gray matter: neurosomas, dendrites, and synapses
Forms cortex (surface layer over cerebrum and cerebellum)
Forms nuclei deep within brain
-White matter: bundles of myelinated axons
Lies deep to cortical gray matter, opposite relationship in the spinal cord
Composed of tracts, or bundles of axons, that connect one part of the brain to another, and to the spinal cord
68
Define and identify the meninges, and describe their function
- Meninges: three connective tissue membranes that envelop the brain
- Lie between the nervous tissue and bone
- As in spinal cord, they are the dura mater, arachnoid mater, and the pia mater
- They protect the brain and provide structural framework for its arteries and veins
69
Describe the relationship between the cranial meninges (specifically the dura mater) and cranial bones
- Cranial dura mater has two layers: outer periosteal and inner meningeal
- These layers are separated by dural sinuses, which collect blood circulating through brain
- No epidural space is present in the cranium
- The dura mater is not directly attached to bone except for in the following places: around foramen magnum of occipital bone, sella turcica, crista galli of ethmoid bone, and sutures of the skull
70
Describe ventricles and define CSF and ependyma
Ventricles: four internal chambers within brain that are filled with CSF:
-Lateral ventricles (2)
-3rd ventricle
-4th ventricle
Ependyma: neuroglia that lines ventricles and covers choroid plexus; filters plasma producing cerebrospinal fluid.
Cerebrospinal fluid (CSF): clear, colorless liquid that fills the ventricles and canals of CNS.
71
Describe the details of CSF production, its circulation within the central nervous system, and it ultimate reabsorption into the bloodstream.
- Cerebrospinal fluid (CSF): clear, colorless liquid that fills the ventricles and canals of CNS
- Brain produces and absorbs 500 mL/day (100 to 160 mL normally present at one time). 40% formed in subarachnoid space external to brain; 30% by the general ependymal lining of the brain ventricles; 30% by the choroid plexuses.
- Production begins with filtration of blood plasma through capillaries of the brain
- Ependymal cells modify the filtrate, so CSF has more sodium and chloride than plasma, but less potassium, calcium, glucose, and very little protein
- Cilia on ependymal cells move CSF
- CSF is reabsorbed by arachnoid villi (granulations)
72
Describe the functions of CSF
Buoyancy
Protection
-Protects the brain from striking the cranium when head is jolted
-Shaken child syndrome and concussions do occur from severe jolting
-Chemical stability
-The flow of CSF rinses away metabolic wastes from nervous tissue and homeostatically regulates its chemical environment
73
Describe the importance of the blood brain barrier
- The brain is only 2% of adult body weight, but receives 15% of the blood
- Neurons have a high demand for ATP, and therefore, oxygen and glucose, so a constant supply of blood is critical
- A 10-second interruption of blood flow may cause loss of consciousness
- A 1-2 minute interruption can cause significant impairment of neural function
- Going 4 minutes without blood causes irreversible brain damage
74
Define the brain barrier system and what two points must be guarded
- Brain barrier system: regulates what substances can get from bloodstream into tissue fluid of the brain
- Although blood is crucial, it can also contain harmful agents
- Two points of entry must be guarded:
1) Blood capillaries throughout the brain tissue
2) Capillaries of the choroid plexus
75
Define and describe the blood-brain barrier
- Blood–brain barrier: protects blood capillaries throughout brain tissue
- Consists of tight junctions between endothelial cells that form the capillary walls
- Astrocytes reach out and contact capillaries with their perivascular feet
- Anything leaving the blood must pass through the cells, and not between them
- Endothelial cells can exclude harmful substances from passing to the brain tissue while allowing necessary ones to pass
76
Define and describe the blood-CSF barrier
Blood–CSF barrier: protects brain at the choroid plexus
| Forms tight junctions between the ependymal cells
77
Brain barrier system is highly permeable to water, glucose, and what?
lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics
78
List the components of the brainstem
Medulla, midbrain, pons
79
Describe the medulla oblongata
-Begins at foramen magnum of skull
-Slightly wider than spinal cord
-Four pairs of cranial nerves begin or end in medulla: VIII (in part), IX, X, and XII
-All ascending and descending fibers connecting brain and spinal cord pass through medulla
-Contains the Pyramids: large motor tracts from cerebrum to spinal cord.
-Have the decussation of pyramids.
Some Autonomic Functions:
-Cardiovascular (Cardiac & Vasomotor) center
-Respiratory center
-Reflex centers for coughing, sneezing, swallowing, and vomiting
80
Describe the pons
Cranial nerves V, VI, VII, and VIII
81
Describe the midbrain
- Regulates auditory and visual reflexes “startle reflex”
- Contains the cerebral aqueduct; a hollow tube that connects the third and fourth ventricles
- Contains motor nuclei of two cranial nerves that control eye movements: CN III (oculomotor) and CN IV (trochlear)
82
Describe the location and structure of the reticular formation
- Loose web of gray matter that runs vertically through all levels of the brainstem
- Occupies space between white fiber tracts and brainstem nuclei
- Has connections with many areas of cerebrum
- More than 100 small neural networks without distinct boundaries
83
List the functions of the reticular formation
Somatic motor control, cardiovascular control, pain modulation, sleep and consciousness, and habituation (filters out stimuli)
84
Describe the reticular formation's functions
1) Somatic motor control
- Adjust muscle tension to maintain tone, balance, and posture, especially during body movements
- Central pattern generators for breathing & swallowing
- Central pattern generators: neural pools that produce rhythmic signals to the muscles of breathing and swallowing
- Relay signals from eyes and ears to cerebellum
- Integrate visual, auditory, balance and motion stimuli into motor coordination
- Gaze centers: allow eyes to track and fixate on objects
2) Cardiovascular control
- Cardiac and vasomotor centers of medulla oblongata
3) Pain modulation
- Some pain signals ascend through the reticular formation
- Some descending analgesic pathways begin in the reticular formation
4) Sleep and consciousness
- Reticular activating system alerts cerebral cortex to awaken from sleep; maintains consciousness & alertness
- Injury here can result in irreversible coma
- Habituation: filters out weak stimuli
- Reticular activating system filters out repetitive or weak stimuli such as background noise (filters out about 99% of all stimuli)
85
Define central pattern generators and where they're found
Neural pools that produce rhythmic signals to the muscles of breathing and swallowing. Can be found in the reticular formation
86
Describe the anatomy of the cerebellum.
- Contains more than half of all brain neurons; about 100 billion
- Superficial cortex of gray matter with deep nuclei; white matter is called arbor vitae
87
Describe the functions of the cerebellum
-Highly important for motor coordination
-Aids in learning and motor skills
-Maintains muscle tone and posture
-Lesions can cause ataxia: clumsy, awkward gait
-Cerebellum has long been known to be important for motor coordination and locomotor ability
-Recent studies have revealed several sensory, linguistic, emotional, and other nonmotor functions like perceiving space and recognizing objects from different views
-Keeping judge of elapsed time and maintaining tapping rhythm
-Planning, scheduling, and emotion control
> Many hyperactive children have small cerebellums
88
Name the three major components of the diencephalon
Thalamus, hypothalamus, epithalamus
89
Describe the hypothalamus and its functions
- Forms part of the walls and floor of the third ventricle
- Controls and integrates activities of the Autonomic Nervous System and Endocrine System
- Controls the pituitary gland
- Produces hormones for labor contractions
- Regulates rage, aggression, pain, pleasure & arousal
- Hunger, thirst & satiety centers
- Controls body temperature (thermoregulation)
- Regulates daily patterns of slee
90
Describe the functions of the epithalamus
Pineal gland: Produces melatonin at night; promotes sleepiness & sets biological clock
91
Describe the functions of the thlamus
- Two thalami are joined medially by intermediate mass
| - “Gateway to the cerebral cortex”: nearly all input to the cerebrum passes through the thalamus
92
There is a limbic system (the emotional or affective brain) within each cerebral hemisphere, which contains what three things?
Cingulate gyrus: aids in expressing emotions
Hippocampus: memory functions
Amygdala: emotion functions
93
Identify the five lobes of the cerebrum
The frontal lobe, the parietal lobe, the occipital lobe, and the temporal lobe. The fifth lobe, the insula or Island of Reil, lies deep within the lateral sulcus.
94
Describe the location and functions of the limbic system.
-Emotional or affective brain
-Prominent components:
1) Cingulate gyrus: aids in expressing emotions
2) Hippocampus: memory functions
3) Amygdala: emotion functions
-There is a limbic system in each cerebral hemisphere
-Limbic system structures have centers for both gratification and aversion
Gratification: sensations of pleasure or reward
Aversion: sensations of fear or sorrow
95
Describe the location and functions of the basal nuclei
- Basal nuclei: masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus
- Control large automatic movements of skeletal muscles (unconscious body movements and facial expressions)
- Uses a neurotransmitter that is inhibitory
96
Describe the part of the brain that's associated with language
- Language includes several abilities: reading, writing, speaking, and understanding words
- Wernicke area
- Usually in left hemisphere
- Permits recognition of spoken and written language
- When we intend to speak, Wernicke area formulates phrases and transmits plan of speech to Broca area
- Generates motor program for the muscles of the larynx, tongue, cheeks, & lips for speaking and for hands when signing
- Transmits program to primary motor cortex for commands to the lower motor neurons that supply relevant muscles
- Affective language area usually in right hemisphere
- Lesions produce aprosody (flat emotionless speech)
97
Describe the part of the brain that's associated with sensation
- Primary sensory cortex: sites where sensory input is first received and one becomes conscious of the stimulus
- Association areas that are near primary sensory areas process and interpret that sensory information
- Multimodal association areas receive input from multiple senses and integrate this into an overall perception of our surroundings
98
What part of the brain is associated with vision?
- Visual primary cortex (occipital lobe)
| - Visual association area: makes cognitive sense of visual stimuli
99
What parts of the brain are associated with hearing?
- Primary auditory cortex
| - Auditory association area: Recognizes spoken words, a familiar piece of music, or a voice on the phone
100
What parts of the brain are associated with equilibrum?
- Signals for balance and sense of motion: to cerebellum
- Association cortex (lateral sulcus near the lower end of the central sulcus): consciousness of our body movements and orientation in space
101
What parts of the brain are associated with taste and smell?
Gustatory (taste) signals received by parietal lobe and insula
Olfactory (smell) signals received by the temporal lobe and frontal lobe
102
What parts of the brain are associated with emotions?
- Emotional feelings and memories are interactions between prefrontal cortex and diencephalon
- Prefrontal cortex: seat of judgment, intent, and control over expression of emotions
- Feelings (e.g., fear) arise from hypothalamus and amygdala
103
Describe the parts of the brain associated with motor control
- Motor association (premotor) area of frontal lobes is where we plan our behavior (intention to contract a muscle)
- Where neurons compile a program for degree and sequence of muscle contraction required for an action
- Program transmitted to neurons of the precentral gyrus (primary motor area)
- These neurons send signals to the brainstem (most fibers decussate in medulla) and then the descending tracts in spinal cord to skeletal muscles
- Basal nuclei and cerebellum are also important in muscle control
104
What are the three types of functional areas?
- Motor areas: control voluntary movement
- Sensory areas: conscious awareness of sensation
- Association areas: integrate diverse information
105
Cognition is accomplished by what?
Distributed association areas of cerebral cortex
106
True or false: Conscious behavior involves the entire cortex
True
107
The _____ lobe helps us think about the world, and plan and execute appropriate behaviors
frontal
108
The ______ lobe helps us identify stimuli (identify familiar objects and faces)
temporal
109
The ______ lobe helps us perceive and attend to stimuli
parietal
110
The _____ cortex is the most complicated region and contains working memory needed for judgment, persistence, and conscience (development depends on feedback from social environment).
prefrontal
111
Define and describe cerebral lateralization
- The difference in the structure and function of the cerebral hemispheres
- Lateralization differs with age and sex
- Children more resilient to lesions on one side
- Males exhibit more lateralization than females & suffer more functional loss when one hemisphere is damaged
112
Describe the functions of the corpus callousm
- Allows the two hemispheres to communicate & coordinate their functions
- If damaged, information processed in one hemisphere unable to reach the other hemisphere
113
Discuss the functional differences between the right and left cerebral hemispheres.
1) Left hemisphere (typically categorical)
Specialized for spoken and written language
Sequential and analytical reasoning (math and science)
Breaks information into fragments and analyzes it
2) Right hemisphere (typically representational)
Seat of imagination and insight
Musical and artistic skill
Perception of patterns and spatial relationships
Comparison of sights, sounds, smells, and taste
114
List the 12 cranial nerves by name and number.
1) Olfactory nerve
2) Optic nerve
3) Oculomotor nerve
4) Trochlear nerve
5) Trigeminal nerve
6) Abducens nerve
7) Facial nerve
8) Vestibulocochlear nerve
9) Glossopharyngeal nerve
10) Vagus nerve
11) Accessory (spinal) nerve
12) Hypoglossal nerve
115
Describe the specific functions of cranial nerves 1-3
1) Olfactory nerve: sensory
Function: smell (sensory only)
Goes through: olfactory foramina of the cribriform plate of the ethmoid bone
2) Optic nerve: sensory
Function: vision (sensory only)
Goes through: optic canal of the sphenoid bone
3) Oculomotor nerve: motor
Function: movement of the eyeball
Goes through: superior orbital fissure of the sphenoid bone.
Controls: superior rectus, interior rectus, medial rectus, and inferior oblique
116
Describe the specific functions of cranial nerves 4-6
4) Trochlear nerve: motor
Function: movement of the eyeball
Travels through: superior orbital fissure of sphenoid bone
Controls: superior oblique muscle
5) Trigeminal nerve: both (mixed)
Functions: sensations of the face; chewing
Controls: masseter and temporalis
6) Abducens nerve: motor
Function: movement of the eyeball laterally
Goes through: superior orbital fissure of sphenoid bone
Controls: lateral rectus muscle of the eye
117
Describe the specific functions of cranial nerves 7-9
7) Facial nerve: both (mixed)
Functions: facial expression; taste
Muscles: all of the muscles of facial expression
8) Vestibulocochlear nerve: sensory
Functions: equilibrium and hearing
9) Glossopharyngeal nerve: both (mixed)
Functions: taste; movement of the pharynx during swallowing and speech, and secretion of saliva
118
Describe the specific functions of cranial nerves 10-12
10) Vagus nerve: both (mixed)
Functions: taste; swallowing, coughing, and parasympathetic stimulation [of the heart and digestive tract]
11) Accessory (spinal) nerve: motor
Functions: swallowing, movement of the head and shoulders
Controls: sternocleidomastoid and trapezius
12) Hypoglossal nerve: motor
Functions: movement of the tongue during speech and swallowing.
Controls: genioglossus muscle
119
Explain how the autonomic and somatic nervous systems differ in form and function.
1) Autonomic nervous system:
Controls glands, cardiac muscle, and smooth muscle
Involuntary: without our conscious intent or awareness
2) Somatic nervous system
Controls skeletal muscles
Voluntary: with our conscious intent or awareness
120
Describe a visceral reflex arc (baroreflex) including structural and function details of sensory and motor components.
1) High blood pressure detected by arterial stretch receptors
2) Afferent neuron carries signal to CNS
3) Efferent signals on vagus nerve of ANS travel to the heart
4) Heart rate slows, ↓ blood pressure
121
Describe the sympathetic division of the autonomic nervous system
- Prepares body for physical activity: exercise, trauma, arousal, competition, anger, or fear
- “Fight-or-flight”
- 4 E’s (emergency, excitement, exercise, embarrassment).
- Increases HR & BP
- Increases airflow (increases breathing rate and causes dilation of bronchiole tubes)
- Blood distributed more to skeletal muscles and less to digestive, kidneys, skin
- Increases blood glucose by breaking down glycogen in liver
- Causes dilation of pupil
122
Describe the parasympathetic division of the autonomic nervous system
- Calms many body functions reducing energy expenditure and assists in bodily maintenance
- “Resting and digesting” state
- SLUDD (normal salivation, lacrimation, urination, digestion, defecation).
- Opposite effects to sympathetic.
123
Describe acetylcholine in relation to the somatic and autonomic nervous systems; what neurons secrete it?
- Acetylcholine (ACh) is secreted by all preganglionic neurons in both divisions and by the postganglionic parasympathetic neurons
- Axons that secrete ACh are called cholinergic fibers
- Any receptor that binds ACh is called a cholinergic receptor
- Inhibitory
124
Describe norepinephrine in relation to the somatic and autonomic nervous systems; what neurons secrete it?
- Norepinephrine (NE) is secreted by nearly all sympathetic postganglionic neurons
- Called adrenergic fibers
- Receptors for NE are called adrenergic receptors
- Excitatory
125
Define autonomic tone and contrast parasympathetic tone and sympathetic tone.
- Autonomic tone: normal background rate of activity that represents the balance of the two systems according to the body’s needs
1) Parasympathetic tone:
- Maintains smooth muscle tone in intestines
- Holds resting heart rate down to about 70 to 80 beats per minute
2) Sympathetic tone:
- Keeps most blood vessels partially constricted and maintains blood pressure
126
Describe the anatomy of the sympathetic nervous system, including the locations the motor neurons exit the CNS, ganglia locations, and the ganglionic and effector neurotransmitters.
- Preganglionic somas in lateral horns lead to nearby sympathetic chain of ganglia
- Each ganglion is connected to a spinal nerve by two branches: communicating rami
- Norepinephrine (NE) is secreted by nearly all sympathetic postganglionic neurons; Acetylcholine (ACh) is secreted by all preganglionic neurons in both divisions.
127
Describe the anatomy of the parasympathetic nervous system, including the locations the motor neurons exit the CNS, ganglia locations, and the ganglionic and effector neurotransmitters.
- Preganglionic fibers end in terminal ganglia in or near target organs
- Acetylcholine (ACh) is secreted by all preganglionic neurons in both divisions and by postganglionic parasympathetic neurons
128
The sympathetic nervous system has _____ preganglionic fibers and _____ postganglionic fibers
Short; long
129
The parasympathetic nervous system has _____ preganglionic fibers and _____ postganglionic fibers
Long; short
130
Discuss the characteristics of the adrenal glands, the two layers of the adrenal glands, and how they're related to the sympathetic nervous system.
- Paired adrenal glands located on superior poles of kidneys
- Each has two layers with different functions:
1) Adrenal cortex (outer layer)
- Secretes steroid hormones
2) Adrenal medulla (inner core)
- Consists of modified postganglionic neurons (anaxonic) that releases epinephrine and norepinephrine.
- Norepinephrine is secreted by nearly all sympathetic postganglionic neurons, and can be regarded as the primary hormone of the sympathetic nervous system (since it prepares your body for “flight or fight”)
131
Discuss the reasons how autonomic neurons have contrasting effects on organs.
1) Sympathetic and parasympathetic fibers secrete different neurotransmitters (norepinephrine and acetylcholine)
2) The receptors on target cells vary
- Target cells respond to the same neurotransmitter differently depending on the type of receptor they have for it
- There are two different classes of receptors for acetylcholine and two classes or receptors for norepinephrine
132
Give examples of control using dual innervation (both sympathetic and parasympathetic) and without dual innervation (sympathetic only).
1) Dual innervation: Parasympathetics increase salivary serous cell secretion, sympathetics increase salivary mucous cell secretion
2) Sympathetic only: Regulation of blood pressure and routes of blood flow
133
Describe the four ways in which the autonomic nervous system is influenced by the central nervous system.
- The ANS is regulated by several levels of CNS:
1) Cerebral cortex has an influence: anger, fear, anxiety; powerful emotions influence the ANS because of the connections between our limbic system and the hypothalamus
2) Hypothalamus: major visceral motor control center
- Has nuclei for primitive functions: hunger, thirst, sex
3) Midbrain, pons, and medulla oblongata contain:
- Nuclei for cardiac and vasomotor control, salivation, swallowing, sweating, bladder control, and pupillary changes
4) Spinal cord reflexes
- Defecation and micturition reflexes are integrated in spinal cord
- If the spinal cord is damaged, the smooth muscle of bowel and bladder is controlled by autonomic reflexes built into the spinal cord
134
Define sensory receptor and sense organ.
1) Sensory receptor: a structure specialized to detect a stimulus
2) Sense organ: nerve tissue surrounded by other tissues that enhance response to a certain type of stimulus.
135
Explain the main purpose of receptors and what a receptor potential is used for.
- Sensory input is vital to the integrity of personality and intellectual function, and sensory receptors are structures specialized to detect stimuli.
- Receptor potential is a small local electrical change on a receptor cell brought about by a stimulus, which results in release of neurotransmitter or action potentials to the CNS, and when this reaches is CNS is when you become conscious of the stimuli.
136
Define sensation.
A subjective awareness of the stimulus
137
List the four kinds of information obtained from sensory receptors.
Modality, location, intensity, duration
138
Define phasic receptors and tonic receptors.
1) Phasic receptors: adapt rapidly; initial burst of action potentials, then slow or stop even though the stimulus continues
- Smell, hair movement, and cutaneous pressure
2) Tonic receptors: adapt slowly; generate nerve signals more steadily throughout presence of stimulus
- Proprioceptors: body position, muscle tension, and joint motion
139
Outline three ways of classifying receptors.
1) By modality
- Thermoreceptors, photoreceptors, nociceptors, chemoreceptors, and mechanoreceptors
2) By origin of stimuli
- Exteroceptors: detect external stimuli
- Interoceptors: detect internal stimuli
- Proprioceptors: sense body position and movements
3) By distribution
- General (somesthetic) senses: widely distributed
- Special senses: vision, hearing, equilibrium, taste, and smell
140
Describe unencapsulated nerve endings and encapsulated nerve endings.
1) Unencapsulated nerve endings: lack connective tissue wrappings
- Free nerve ending for pain and temperature
- Tactile discs for light touch and texture
- Hair receptors coil around a hair follicle
2) Encapsulated nerve endings: are wrapped by glial cells or connective tissue
- Wrapping enhances sensitivity or selectivity of response; examples include:
- Tactile (Meissner) corpuscles
- Krause end bulbs (in mucous membranes)
- Bulbous corpuscles; tonic
- Lamellar (Pacinian) corpuscles; phasic
141
Define pain and describe fast pain and slow pain.
1) Pain: caused by tissue injury or noxious stimulation, and typically leading to evasive action
2) Fast pain travels myelinated fibers at 12 to 30 m∕s
- Sharp, localized, stabbing pain
3) Slow pain travels unmyelinated fibers at 0.5 to 2 m∕s
- Longer-lasting, dull, diffuse feeling
142
Describe somatic pain and visceral pain.
1) Somatic pain: have deep and superficial
- Deep: bones, joints, muscles (arthritis, sprains, bone fractures)
- Superficial: from skin (cuts, burns, insect stings)
2) Visceral pain: from the viscera
- Stretch, chemical irritants, or ischemia of viscera (heart attacks)
143
List 4 chemicals that stimulate pain fibers.
Bradykinin, histamine, prostaglandin, and serotonin
144
Define referred pain and be able to give examples.
- Referred pain: pain in viscera often mistakenly thought to come from the skin or other superficial site
- Ex: Heart pain felt in shoulder or arm because both send pain input to spinal cord segments T1 to T5
145
List the five primary taste sensations.
Salty, Sweet, Umami, Sour, Bitter
146
List what other sensations influence taste
Taste is influenced by smell, thermoreceptors, mechanoreceptors, & nociceptors
147
List the three cranial nerves that carry information on taste and their destinations.
- Facial nerve, Glossopharyngeal nerve, and Vagus nerve
- All fibers go to medulla
- 2 destinations:
- -Hypothalamus and Amygdala (Limbic system)
- -Thalamus relays signals to Gustatory cortex (Insula lobe)
148
Describe the olfactory mucosa and the basic olfactory pathways.
1) Olfactory mucosa
- Located on superior concha, nasal septum, and roof of nasal cavity
- Average 2,000 to 4,000 odors distinguished
2) Basic olfactory pathways:
- Olfactory cells synapse in olfactory bulb
- Information travels on axons which form the olfactory tracts
- Destinations:
a) Primary olfactory cortex (temporal lobe)
b) Limbic system (hippocampus and amygdala)
c) Hypothalamus
- Fibers reach back to olfactory bulbs where cells may be inhibited
- Odors change under different conditions
149
Describe the gross anatomy of the ear.
- Ear has three sections: outer, middle, and inner ear
- First two are concerned only with the transmission of sound to the inner ear
- Inner ear: vibrations converted to nerve signals
150
Describe the three components of the outer ear
- Conducts vibrations to the tympanic membrane (eardrum)
1) Auricle (pinna) directs sound down the auditory canal; shaped and supported by elastic cartilage
2) Auditory canal (external acoustic meatus): passage leading through temporal bone to tympanic membrane
3) Cerumen (earwax): mixture of secretions of ceruminous and sebaceous glands and dead skin cells
151
Describe the four main components of the middle ear
- Located in the air-filled tympanic cavity in temporal bone
1) Tympanic membrane (eardrum)
- Vibrates freely in response to sound
2) Tympanic cavity
- Space only 2 to 3 mm wide between outer and inner ears
- Contains auditory ossicles
3) Auditory (eustachian) tube connects middle ear to nasopharynx
- Equalizes air pressure on both sides of tympanic membrane
- Normally closed, but swallowing or yawning open it
- Allows throat infections to spread to middle ear
4) Auditory ossicles
- Malleus, Incus, Stapes
- Stapes rests on oval window; where inner ear begins
152
Describe the four main components of the inner ear
1) Bony labyrinth: passageways in temporal bone
2) Membranous labyrinth: fleshy tubes lining bony labyrinth
- Filled with endolymph: similar to intracellular fluid
- Floating in perilymph: similar to cerebrospinal fluid
3) Vestibule and three semicircular ducts
4) Cochlea: organ of hearing; 3 fluid-filled chambers separated by membranes
153
Describe the three components of the cochlea
1) Scala vestibuli: superior chamber
- Begins at oval window & spirals to apex; filled with perilymph
2) Scala tympani: inferior chamber
- Begins at apex & ends at round window; filled with perilymph
3) Scala media (cochlear duct): middle chamber
- Floor formed by basilar membrane; top by vestibular membrane; filled with endolymph
- Contains spiral organ; organ of Corti converts vibrations into nerve impulses
154
Explain how the ear converts vibrations to nerve signals
- Tympanic membrane vibrates
- Causes ossicles to vibrate; they concentrate the energy
- Stapes pushes oval window which moves the perilymph in Scala vestibuli
- This causes vibration of basilar membrane and moves hair receptors against the tectorial membrane
- Movement of hair receptors sets off an electrical signal
- Sensory fibers begin at the bases of hair cells
- Organ of Corti converts vibrations into nerve impulses
155
Explain how the ear discriminates between sounds of different intensity and pitch.
- Variations in loudness (amplitude) cause variations in the intensity of cochlear vibrations
- Soft sound produces relatively slight up-and-down motion of the basilar membrane
- Louder sounds make the basilar membrane vibrate more vigorously
- Triggers higher frequency of action potentials
- Brain interprets this as louder sound
- Pitch depends on which part of basilar membrane vibrates
156
Explain how the vestibular apparatus enables the brain to interpret the body’s position and movements.
- The vestibular apparatus constitutes hair receptors for equilibrium
- Three semicircular ducts that detect only angular acceleration
- Two chambers (Saccule and Utricle) that detect static equilibrium and linear acceleration
157
Describe the pathways taken by auditory signals to the brain.
- Organ of Corti converts vibrations into nerve impulses
- Axons lead away from cochlea as the cochlear nerve
- Joins with the vestibular nerve to form the vestibulocochlear nerve (cranial nerve VIII)
- Each ear sends nerve fibers to both sides of the pons, then midbrain
- From midbrain to thalamus; ends in primary auditory cortex (temporal lobe)
- Auditory system has extensive decussations, so damage to one side of cortex does not cause unilateral hearing loss
158
Describe the pathways taken by vestibular signals to the brain and what four destinations they go to
- Hair cells of saccule, utricle, and semicircular ducts synapse on vestibular nerve (part of CN VIII); fibers end in pons and medulla
- Main Destinations:
1) Cerebellum: information for control of head and eye movements, muscle tone, and posture
2) Nuclei of oculomotor, trochlear, and abducens nerves (CN III, IV, and VI): coordinates eye movement
3) Thalamus; relay to cerebral cortex for awareness of position and motor control of head and body
4) Spinal cord and Reticular formation
159
Describe the eyelids (palpebrae)
- Consist of orbicularis oculi muscle and tarsal plate covered with skin outside and conjunctiva inside
- Tarsal glands secrete oil that reduces tear evaporation
- Eyelashes help keep debris from eye
160
List the three accessory structures of the orbit
Eyelids (palpebrae), conjunctiva, and lacrimal apparatus,
161
Describe the conjunctiva of the eye
- A transparent mucous membrane that lines eyelids and covers anterior surface of eyeball, except cornea
- Richly innervated and vascular (heals quickly)
- Secretes a thin mucous film that prevents the eyeball from drying
162
What does the lacrimal apparatus of the eye do?
- Makes, distributes and drains tears into nasal cavity.
| - Tears wash and lubricate eye, deliver O2 and nutrients, and prevent infection with a bactericidal lysozyme
163
Describe the extrinsic muscles of the eye, their functions, and the cranial nerve that innervates each.
-Six extrinsic muscles attach to exterior surface of eyeball: Superior, inferior, lateral, and medial rectus muscles, superior and inferior oblique muscles
-Innervated by cranial nerves:
CN IV innervates superior oblique
CN VI innervates lateral rectus
CN III innervates other four extrinsic muscles
-Superior, inferior, medial, and lateral rectus muscles move the eye up, down, medially, and laterally (respectively)
-Superior and inferior obliques turn the “twelve o’clock pole” of each eye toward or away from the nose; they also produce slight elevations and depressions of the eye
164
Describe the three tunics of the eye.
1) Tunica fibrosa: outer fibrous layer
- Sclera: dense, collagenous white of the eye
- Cornea: transparent region modified sclera in front of eye
2) Tunica vasculosa (uvea): middle vascular layer
- Choroid: highly vascular, deeply pigmented layer behind retina
- Ciliary body: extension of choroid; a muscular ring around lens; supports lens and iris and secretes aqueous humor
- Iris: colored diaphragm controlling size of pupil (opening)
- Color controlled by amount of melanin
3) Tunica interna: retina and beginning of optic nerve
165
Discuss the aqueous humor and vitreous humor of the eye
1) Aqueous humor
- Serous fluid secreted by ciliary body into posterior chamber; posterior to cornea, anterior to lens
- Reabsorbed by scleral venous sinus at same rate it is secreted
2) Vitreous body (humor)
- Fills vitreous chamber
- Jelly fills space between lens and retina
- Holds retina in place
166
Discuss the structure of the retina
- Retina converts light energy into action potentials
- Attached to eye only at optic disc (posterior exit of optic nerve) and ora serrata (anterior edge of retina)
- Optic disc: no receptors so also called the blind spot
- Pressed against rear of eyeball by vitreous humor
- Detached retina causes blurry areas of vision and can lead to blindness
- Macula lutea: patch of cells on visual axis of eye (highest acuity)
- Fovea centralis: pit in center of macula lutea
- Blood vessels of the retina
167
Discuss the two types of receptor cells of the retina
1) Rod cells
- Night, or scotopic, vision or monochromatic vision
- Respond to dim light
- Used in peripheral vision
2) Cone cell
- Color, photopic, or day vision
- Produce high-acuity color vision
- Concentrated in the macula lutea (especially in the fovea centralis)
168
Explain how the optical system of the eye creates an image on the retina.
- Light passes through lens to form tiny inverted image on retina; this is thanks to refraction.
- Iris diameter controlled by two sets of smooth muscle
a) Parasympathetic stimulation narrows pupil
b) Sympathetic stimulation widens pupil
- Pupillary constriction and dilation occurs:
a) When light intensity changes
b) When gaze shifts between distant and nearby objects
169
Describe the near response and list the three processes used.
1) Convergence of eyes
2) Constriction of pupil
3) Accommodation of lens: change in the curvature of the lens that enables you to focus on nearby objects
- Ciliary muscle contracts, suspensory ligaments slacken, and lens takes more convex (thicker) shape
170
Describe the visual projection pathway.
- Two optic nerves combine to form optic chiasm
- Half the fibers cross over to the opposite side of the brain (hemidecussation) and chiasm splits to form optic tracts
- Right cerebral hemisphere sees objects in left visual field because their images fall on the right half of each retina
- Each side of brain sees what is on side where it has motor control over limbs
- Pathway goes through thalamus; major destination primary vision cortex (occipital lobe)
171
Describe the eye disorders of glaucoma and cataracts
1) Glaucoma: elevated pressure within the eye due to obstruction of scleral venous sinus and improper drainage of aqueous humor
- Leads to death of retinal cells due to compression of blood vessels and lack of oxygen
2) Cataracts: clouding of the lens of the eye
- Typically occurs in the elderly
172
Describe the eye disorders of macular degeneration and detached retina
1) Macular degeneration:
- Leads to a ‘missing’ or blurry spot in the center of the field of vision
- Typically occurs with advanced age
2) Detached retina:
- When the retina is no longer attached to the eye at optic disc (posterior exit of optic nerve) and/or ora serrata (anterior edge of retina)
- Detached retina causes blurry areas of vision and can lead to blindness
