nervous system Flashcards
(116 cards)
0
Q
2 parts of PNS
A
Somatic Nervous system
Autonomic nervous system
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Q
Peripheral nervous system
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All nerves that go in or out if CNS
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Q
Autonomic nervous system
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Controls smooth and cardiac muscle
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Q
Somatic nervous system
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Controls motion, skeletal muscle, motor neurons
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Q
Types of neuroglia
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Astrocytes (CNS) Oligodendrocytes (CNS) Microglial cells (CNS) Ependymal cells (CNS) Satellite cells (PNS) Schwann cells (PNS)
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Q
Neuroglia
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- Non-nervous supporting cells
- provide supportive scaffolding for neurons
- cover all non synaptic parts of neurons
- insulates them
- keeps electrical activities if adjacent neurons from interfering with each other
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Q
Oligodendrocytes
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- fewer branches than astrocytes
- wrap their cell processes around the thicker axons in CNS, producing insulating coverings called myelin sheaths
- type of neuroglia in CNS
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Q
Schwann Cells
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Surround all axons in PNS and form Myelin sheaths around many of these axons
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Q
Myelin sheath
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- produced by Oligodendrocytes in CNS and Schwann cells in PNS
- segmented structures composed of the lipoprotein myelin
- Insulates nerves (prevents leakage of electrical current from the axon) -speeds up nerve impulse, makes it more energy efficient
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Q
Neurons
A
Nerve cells
- Conduct electrical signals from one part of the body to another
- Transmitted along plasma membrane in the from or nerve impulses or action potentials.
- extreme longevity
- don’t divide
- high metabolic rate
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Q
Sensory neurons
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- Afferent neurons
- make up sensory division of PNS
- -transmit impulses toward the CNS from sensory receptors in PNS
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Motor neurons
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- efferent neurons
- motor division of PNS
- carry impulses away from CNS to effector organs (muscles or glands)
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Q
Parts of a neuron
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Cell body
Big portion
Dendrites
Tips of cell body has these
receives information
Axon
Long portion
Contains axon terminals
Function: carries the nerve impulse
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Q
Demyelination disorders
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Multiple sclerosis
Diphtheria
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Q
Multiple sclerosis
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Destruction of the myelin sheath
Loss of vision, speech, balance, and coordination
Often progressive
Cause unknown-virus leads to immune system attacking Schwann cells?
Multiple locations; sclerosis- hardened scars
2.6 million cases worldwide
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Q
Diphtheria
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Bacteria makes toxin that damages Schwann cells
U.S usually vaccinated
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Q
Central nervous system
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Brain and spine
Receives messages from PNS
Analyzes them, then sends out signals of how to respond
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Q
Synapse
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Site at which neurons communicate
Most transmit info through chemical messengers
Some transmit signals electrically
Determine direction of info flow through nervous system
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Q
Presynaptic neuron
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Neuron that conducts signals toward a synapse
Most neurons function as both post and pre synaptic
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Q
Postsynaptic neurons
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Transmits signals away from the synapse
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Q
Synaptic cleft
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At the synapse, the plasma membranes of the two neurons are separated by this
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Q
Structural classification of neurons
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Grouped according to the number of processes that extend from the cell body
-multipolar, bipolar, or unipolar
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Q
Multipolar
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- many processes extend form the cell body
- all are dendrites except for a single axon
- slightly larger conducting region (almost in equal parts receptive, conducting, and secretory)
- most abundant
- major neuron type in CNS
- most are interneurons that conduct impulses within the CNS
- can be one if a chain of CNS neurons, or a single neuron connecting sensory and motor neurons - some are motor neurons
- conduct impulses along efferent pathways from CNS to an effector
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Q
Bipolar
A
- two processes extend form the cell body, one Is a fused dendrite, the other is an axon
- rare, found in some special sensory organs (olfactory mucosa, eye, ear)
- essentially all are sensory neurons
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Unipolar
- one process, forms central and peripheral processes, together comprise an axon
- found mainly in the PNS
- common only in the dorsal root ganglia if the spinal cord and the sensory ganglia of cranial nerves
- most are sensory neurons that conduct impulses along afferent pathways to CNS for interpretation
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Peripheral process
Branch on unipolar neuron that extends peripherally to the receptors
Looks like an axon, acts like a dendrite
The central process runs centrally into the CNS, and acts like an axon
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Functional classification of neurons
Grouped functionally according to the direction the nerve impulse travels relative to the CNS
-sensory, motor, interneurons
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Interneurons
- lie between motor and sensory neurons
- multipolar
- confined entirely to the CNS
- link together in chains tht form complex neuronal pathways
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Astrocytes
- star shaped, most abundant neuroglia in CNS
- many radiating processes with bulbous ends
- some ends cling to neurons,bothers to capillaries
- regulating neurotransmitter levels
- signaling increased blood flow through capillaries
- controlling ionic environment around neurons
- help synapses form
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Microglial cells
- smallest and least abundant neuroglia
- elongated body with many pointed projections
- phagocytes, macrophages of the CNS
- engulf invading microorganism or dead/injured neurons
- derived from blood cells called monocytes
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Ependymal cells
- neuroglia
- form a simple epithelium that lines the central cavity of the spinal cord and Brain
- Provide a fairly permeable layer between the cerebrospinal fluid that fills this cavity and the tissue fluid that bathes the cells of the CNS
- bear cilia that help circulate the cerebrospinal fluid
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Satellite cells
- neuroglia of PNS
| - surrounds neuron cell bodies within ganglia
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Gray matter of CNS
- gray colored zone tht surrounds hollow central cavity of CNS
- site where neuron cell bodies are clustered
- synapses occurs here
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White matter of CNS
- contains no neuron cell bodies but millions of axons and neuroglia
- white color comes from myelin sheaths around many of the axons
- consists of axons running between diff parts of the CNS
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Nerve
- cable like organ in PNS
- consists of many axons (nerve fibers) arranged in parallel bundles and enclosed by successive wrappings of connective tissue
- each axon is surrounded by Schwann cells
- endoneurinium, perineurium, epineurium
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Perineurium
In nerve, groups of axons are bound into bundles called nerve fascicles by a wrapping of connective tissue called this
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Epineurium
Whole nerve is surrounded by this tough fibrous sheath
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Endoneurium
-in a nerves the Schwann cells are covered by a delicate layer of loose connective tissue called this
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Reflex arcs
-simple chains of neurons that cause our simplest, reflexive behaviors and reflect the basic structural plan of the nervous system
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Reflexes
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Rapid, automatic motor responses to a stimuli
Can be either somatic reflexes (contraction of skeletal muscle)
Visceral reflexes (activating smooth muscle, cardiac muscle, or glands)
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Five essential components of reflex arc
1. Receptor (site where stimulus acts). Located at the terminal end of peripheral process of a sensory neuron
2. Sensory neuron transmits afferent impulse to CNS
3. Integration center (one or more synapses in the gray matter of CNS)
4. Motor neuron conducts efferent impulses to an effector
5. Effector is the muscle or gland tht responds to the efferent impulses
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Monosynaptic reflex
- simplest
- no interneurons between sensory and motor
- only one synapse
- many skeletal muscles have monosynaptic stretch reflexes,which help maintain equilibrium
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Polysynaptic reflex
- more common
- one or more interneurons are part of the pathway btwn sensory and motor
- at least two synapses
- withdrawal reflexes an example of this
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Neuronal circuits
-interneurons of CNS may be interconnected in multiple ways
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Types of neuronal circuits
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Diverging
Parallel
Serial
converging
Reverberating
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Diverging circuit
- one Presynaptic neuron synapses with several other neurons
- as a result, info is distributed through mult neuronal pathways
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Converging circuit
-many neurons synapse on a single post synaptic neuron
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Reverberating circuit
- one neuron in the circuit receives feedback from another neuron in the same circuit
- a branch off the axon of one neuron circles back and synapses with a previous neuron in the circuit
- signal continues to be sent until either synaptic fatigue or inhibition by another signal interrupts the circuit
- control of many rhythmic activities such as walking and breathing
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Serial processing
- neurons that synapse one on one in a sequence are said to be joined In a series
- pass signal along a single pathway from one neuron to the next like links in a chain
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Parallel processing
- info from a single neuron is sent along two or more parallel pathways
- occurs when a single sensory stimulus results in multiple perceptions
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Ventricles of the brain
- expansions of the brains central cavity, filled with cerebrospinal fluid
- paired lateral ventricles, third ventricle, fourth ventricle,
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Lateral ventricles
- lie in the cerebral hemispheres
- horseshoe shape reflects the bending of the hemispheres during dvlpmnt
- anteriorly, they lie close together and are separated by a thin median membrane called septum pellucidum (transparent wall)
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Third ventricle
- lies in the diencephalon
| - anteriorly connects to each lateral ventricle though an interventricular foramen
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Cerebral aqueduct
- in midbrain
| - thin tubelike central cavity, connects the third and fourth ventricles
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Fourth ventricle
- lies in the brain stem, dorsal to the pons and the superior half of the medulla oblongata
- three openings occur in the walls, paired lateral apertures and the median aperture
- connect the ventricles with the subarachnoid space
- allows cerebrospinal fluid to fill both the ventricles and the subarachnoid space
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Medulla oblongata
- most caudal part of the brain stem
- continuous with the spinal cord at the level of the foramen magnum of the skull
- contains projection fibers
- site of decussation of the pyramids
- relays sensory information to the cerebellum through inferior olivary nuclei
- contains nuclei if cranial nerves (VIII-X and XII)
- contains visceral nuclei controlling heart rate, blood vessel diameter, respiratory rate, vomiting, coughing, etc
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Pyramids
- two longitudinal ridges flank the ventral midline of the medulla
- carry voluntary motor output to the spinal cord
- cross over to the opposite side of the Brain at a point called the decussation of the pyramids
- results in each cerebral hemisphere controlling the voluntary movements of the opposite side of the body
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Pons
- second region of the brain stem
- bulge wedged btwn the midbrain and the medulla oblongata
- forms a ventral bridge between the brain stem and the cerebellum
- contains projection fibers
- pontine nuclei relay info from cerebrum and cerebellum
- contains nuclei of cranial nerves V-VII
- contains reticular formation nuclei
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Midbrain
- part of brainstem, lies between the diencephalon and the pons
- white fiber tracts and relay nuclei in the midbrain connect regions of the CNS
- contains projection fibers
- contains subcortical motor centers
- contains nuclei for cranial nerves III and IV
- contains visual and auditory reflux centers
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Thalamus
- deep brain region
- relays sensory impulses to cerebral cortex for interpretation
- processes the information as it passes through
- either amplify or tone down the signals headed for the cerebral cortex (why you can focus on a single person in a large noisy cafeteria)
- involved in memory processing
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Hypothalamus
- below the thalamus
- main visceral control center of the body
- controls the autonomic nervous system
- regulation of body temperature
- regulation of hunger and thirst sensations
- reg. of sleep wake cycles
- control of the endocrine system
- control of emotional responses
- control of motivational behavior
- formation of memory
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Frontal lobe
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Voluntary movement
Planning movement
Eye movement
Speech production
Executive cognitive functions
Emotional response
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Parietal lobe
General somatic sensation
Spatial awareness of objects, sounds,body parts
Understanding speech
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Occipital lobe
Vision
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Temporal lobe
Hearing
Smell
Object identification
Emotional response, memory
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Insula
Taste
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Cerebral white matter
-via the many fibers of the white matter that the various areas of the cerebral cortex communicate both with one another and with the brain and the spinal cord
Commissural fibers
-connect the corresponding cortices of the two hemispheres
Associative fibers
-connect the cortex of the different parts of same hemisphere
Projection fibers
-connect the cortex to more caudal parts of the CNS
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Deep Cerebral gray matter
Basal nuclei (ganglia)
-control movements in conjunction with the motor cortex
Basal forebrain nuclei
-perform major role in arousal, learning, memory, and motor control (rich in cholinergic fibers)
Claustrum
-function unclear. May integrate info between cerebral cortex and Limbic system
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Visual pathways
Visual info proceeds anteriorly in two streams
Dorsal stream
Ventral stream
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Dorsal stream
Extends though the posterior parietal cortex to the post central gyrus
- perceives spatial relationships among various objects
- "where" pathway
- identifies location of objects
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Ventral stream
Extends through the inferior part of the temporal lobe
- responsible fir recognizing objects, words during reading, and faces
- "what" pathway
- identifies what things are
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Hydrocephalus
Excessive accumulation of CSF in the ventricles or subarachnoid space can exert a crushing pressure on the brain
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Cerebrospinal fluid
- watery broth that fills the subarachnoid space and the central hollow cavities of the brain and spinal cord
- aids in protecting and nourishing the neural tissue
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Pia mater
- layer of delicate connective tissue richly vascularized with fine blood vessels
- clings tightly to the brain surface
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Arachnoid mater
Lies just deep to the dura mater
Surround the brain loosely
Deep to the arachnoid membrane is the subarachnoid space, spanned by weblike threads that hold the arachnoid mater to the underlying pia mater (filled with CSF)
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Meninges
Three connective tissue membranes that lie just external to the brain and spinal cord
- cover and protect CNS
- enclose and protect the blood vessels that supply the CNS
- contain the CSF
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Three meninges
Dura mater
Arachnoid mater
Pia mater
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Dura mater
- strongest of the meninges
- two layer sheet of dense fibrous connective
- Periosteal layer attaches to the internal surface of the skull bones
- meningeal layer(deeper) forms the true external covering of brain
- in several places the meningeal dura mater extends inward to form flat partitions that subdivide the cranial cavity and limit movement of the brain
- falx cerebri
- falx cerebelli
- falx tentorium cerebelli
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Reticular formation
Functional system
- maintains cerebral cortical alertness (reticular activating system)
- filters out repetitive stimuli
- helps regulate skeletal and visceral muscle activity and modulate pain
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Reticular activating system
- maintains consciousness and alertness
- functions in sleep and in arousal from sleep
- severe injury to this causes coma
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Cranial nerves
Twelve
Except for vagus, only innervate head and neck structures
-olfactory, optic oculomotor, trochlear, trigeminal, abducens, facial, vestibulocochlear, glossopharyngeal, vagus, accessory, hypoglossal
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Olfactory nerve
Sensory never of smell
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Optic nerve
Sensory nerve of vision
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Oculomotor nerve
Innervates four of the extrinsic eye muscles( muscles tht move the eyeball in the orbit)
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Trochlear nerve
Innervates an extrinsic eye muscle that hooks through a pulley-shaped ligament in the orbit
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Trigeminal nerve
Provides general sensory innervation to the face and motor innervation to the chewing muscles
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Abducens
Innervates the muscle that abducts the eyeball (turns the eye laterally)
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Facial nerve
Innervates the muscles of facial expression as well as other structures
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Vestibulocochlear nerve
Sensory nerve of hearing and equilibrium
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Glossopharyngeal nerve
Innervate tongue and pharynx
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Vagus nerve
Vagabond
| Wanders beyond the head into the thorax and abdomen
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Accessory nerve
Carries motor innervation to the trapezius and sternocleidomastoid muscles
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Hypoglossal nerve
Innervates the tongue muscles
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Dermatomes
An area of skin Innervated by the sensory fibers of a single spinal nerve (mapped out on body)
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Each spinal nerve connects to the spinal cord by..
A dorsal root and a ventral root
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Nerve plexus
Network of nerves, join one another lateral to the vertebral column forming a plexus
-cervical, brachial, lumbar, and sacral
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Phrenic nerve
Most important nerve from cervical plexus
Innervates diaphragm
Provides sensory and somatic motor innervation to it
If damaged, resp arrest will occur
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Relationships within brachial plexus
Roots transition into trunks (upper, middle, and lower)
Trunks transition into divisions (anterior and posterior)
Divisions transitions into cords (lateral, posterior, medial)
Then nerves
-axillary, musculocutaneous, radial, median, ulnar
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Musculocutaneous nerve
Innervated biceps brachii, brachialis, and coracobrachialis muscles
Enables skin sensation on the lateral forearm
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Median nerve
Innervated most muscles of the anterior forearm and lateral palm
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Ulnar nerve
Innervates most of the intrinsic hand muscles and the skin on the medial side of the hand
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Axillary nerve
Innervates the deltoid and teres minor muscles
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Radial nerve
Innervates almost the entire posterior side of the upper limb
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Radial nerve injury
Results in wrist-drop (inability to extend the hand at the wrist)
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Ulnar nerve injury
Results in clawhand (cant extend fingers)
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Median nerve injury
Hand if benediction (can't flex thumb and next two fingers)
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Femoral nerve
Lumbar plexus
| Innervate muscles of the anterior compartment of the thigh
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Obturator nerve
Lumbar plexus
| Innervate the adductor muscle group
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Sciatic nerve
Sacral plexus
Supplies all of the lower limb except the anterior and medial regions of the thigh
-made up of two nerves
-tibial nerve (supplies posterior)
-common fibular nerve (supplies anterior stuff)
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Preganglionic neuron
Signal the postganglionic
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Postganglionic
Stimulates muscle contraction or gland secretion in the effector organ
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Ganglionic neurons in the parasympathetic
Long preganglianic axon and short postganglionic
| Opposite for sympathetic
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Ganglia
Cluster of neuronal cell bodies in the PNS
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Sympathetic Neurotransmitters
Preganglianic: acetylcholine
Postganglionic: norepinephrine
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Parasympathetic transmitter
Acetylcholine for both
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3 Sympathetic pathways
- preganglionic axon synapses with postganglionic neuron in the sympathetic trunk ganglion at the same level and exits on the spinal nerve at that level
- preganglionic axon ascends or descends in the sympathetic trunk to synapse in another trunk ganglion. Postganglionic fiber exits the sympathetic trunk
- preganglionic axon passes through the sympathetic trunk, exits on a splanchnic nerve, and synapses in a collateral ganglion. Postsynaptic fiber extends from the collateral ganglion to the visceral organ via an autonomic nerve plexus
