Nervous System Flashcards
1
Q
Central Nervous System (CNS)
A
- Command centre
- Brain + spinal cord
- Processes + integrates information
2
Q
Peripheral Nervous System (PNS)
A
- Consists of:
1) Cranial nerves - to/from brain
2) Spinal nerves to/from spinal cord - 2 divisions of PNS:
1) Sensory/afferent division
3
Q
Peripheral Nervous System Divisions
A
1) Sensory/afferent division
- Has sensory receptors that detect stimuli (changes in the internal or external environments)
- Nerves convey impulses TOWARD CNS
2) Motor/Efferent division
- Nerves convey impulses AWAY from CNS
- Innervates (supplies nerves to) effectors = muscles + glands (endocrine or exocrine)
4
Q
Relationship between CNS and PNS
A
Look at diagram
5
Q
Nervous System Organization
A
Diagram
6
Q
Neurons (Nerve cell type)
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- Conduct impulses
- Make up CNS + PNS
- Mostly amitotic (irreplaceable) exceptions = taste, olfaction, memory
- Structures:
1) Cell body
2) Processes from cell body
a) Dendrites
b) Axon
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Q
Cell body (Neurons)
A
- Typical organelles
- RER called Nissl bodies
- Groups/clusters in CNS = nuclei (grey matter)
- Groups/clusters in PNS = ganglia
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Q
Dendrites (Neurons)
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Receive incoming messages + relay to cell body
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Q
Axon (Neurons)
A
- Carries impulses away from cell body
- Axon hillock - where axon meets cell body
- Axon terminal - typically branched with synaptic end bulbs (enlarged tips)
10
Q
Myelinated Axon
A
- Myelinated - wrapped in many layers of cell membrane from Schwann cells (PNS) or oligodendrocytes (CNS)
- Electrical insulation
- Gaps in myelin sheath are called nodes of Ranvier
- Myelinated axon bundles in:
1) CNS = tracts (white matter)
2) PNS = nerves (know the difference)
11
Q
Unmyelinated Axon
A
No myelin
12
Q
Neuroglia (Glial cells) (Nerve Cell Type)
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- Support neurons = can undergo mitosis (prone to cancer - brain tumour)
13
Q
CNS Neuroglia
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1) Oligodendrocytes
2) Microglia
3) Astrocytes
4) Ependymal Cells
14
Q
Oligodendrocytes (CNS neuroglia)
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Produce myelin around axon
15
Q
Microglia (CNS neuroglia)
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- Protective – become phagocytic if detect infected, dead or damaged neurons (because immune cells can’t enter CNS)
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Q
Astrocytes (CNS neuroglia)
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- Surrounded blood capillaries to form part of blood brain barrier (BBB)
- Help control capillary permeability
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Q
Ependymal Cells (CNS neuroglia)
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- Neural epithelium
- Line brain ventricles + central canal of spinal cord
- Secrete cerebrospinal fluid (CSF) + circulate it (cilia)
18
Q
PNS Neuroglia
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1) Schwann Cells
- Form myelin around axons in PNS
2) Satellite Cells
- Surround neuron cell bodies ganglia
- Protection and support
19
Q
Neuron Classification
A
1) Structural/ Anatomical Types:
- Based on number of processes coming off cell body
a) Unipolar
b) Bipolar
c) Multipolar
2) Functional Types:
- Based on direction of impulse conduction
a) Sensory/Afferent neurons
b) Interneurons
c) Motor/Efferent neurons
20
Q
Unipolar
A
- 1 process the divides into two: central + peripheral
- Peripheral end has dendrites = sensory receptors (pain, touch, etc) - reminder is axon
- Always sensory
21
Q
Bipolar
A
- 2 processes: 1 axon, 1 process with dendrites
- Sensory = retina, nose (olfaction)
22
Q
Multipolar
A
- 3 or more processes: 1 axon, many dendrites
- All interneurons + motor neurons
23
Q
Sensory/Afferent Neurons
A
- Mostly unipolar
- From sensory receptors to CNS
24
Q
Interneurons
A
- Within CNS (between sensory + motor)
- 99% of neurons (mostly multipolar)
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Motor/Efferent Neurons
- CNS to effectors (all multipolar)
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Neuronal Junctions (Synapses)
1) Neuronal Junction:
- Neuron to Neuron
- Can be chemical (use neurotransmitters) or electrical (ions)
2) Neuromuscular Junction:
- Motor neuron to skeletal muscle cell
3) Neuroglandular Junction:
- Motor neuron to smooth or cardiac muscle, or a gland
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Chemical Neuronal Synapses
- Most common
- Structures:
1) Presynaptic Neuron
- Neuron bringing impulse
- Has axon terminal with synaptic end bulbs
- Inside end bulb = synaptic vesicles containing neurotransmitter (nt)
- Presynaptic membrane (cell membrane facing space)
2) Synaptic Cleft
- Space between neurons
3) Postsynaptic Neuron
- Receives the signal
- Has postsynaptic membrane = cell membrane of dendrites or cell body with receptors for nt
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Central Nervous System: Protective Features
1) Bone
2) Meninges
3) Cerebrospinal Fluid (CSF)
4) Blood-Brain Barrier (BBB)
5) Cerebral Arterial Circle
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Bone
- Skull and vertebral column
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Meninges
- CT around brain + spinal cord
- Layers:
1) Dura Mater
2) Arachnoid Mater
3) Pia Mater
- Meningitis = inflammation of meninges
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Dura Mater (Outer)
- Brain = 2 fused layers - separated in some places to form spaces = venous (dural) sinuses - contain blood
- Spinal cord - 1 layer
- Deep to dura mater = subdural space - filled with ISF
- Superficial to dura mater = epidural space (spinal cord only) - filled with fat, blood vessels, CT, etc
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Arachnoid Mater (Middle)
- Avascular
- Subarachnoid space:
~contains cerebrospinal fluid (CSF)
~ Web-like strands of CT secure it to Pia mater (below)
- Has arachnoid granulations (brain only)
~ Projections into dural sinuses
~ CSF enters granulations to return to blood
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Pia Mater (Inner)
- On surface of CNS (brain and spinal cord)
| - Vascular
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Cerebrospinal Fluid (CSF)
- Surrounds brain + spinal cord
- In brain ventricles + central canal of spinal cord
- Ventricles:
~ Spaces inside brain (filled with CSF)
~ 2 lateral ventricles (1st and 2nd) - in cerebrum
~ 3rd ventricle - in diencephalon
~4th ventricle - surrounded by pons, medulla oblongata, cerebellum
- Central canal:
~ Space in spinal cord
- Cushions CNS - brain buoyant
- Formed from blood plasma (similar composition)
- Produced by choroid plexuses (blood capillaries) found in each ventricle
- Circulation: LOOK AT DIAGRAM
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Blood-Brain Barrier (BBB)
- 2 cell types:
1) Endothelial cells (of capillaries) with tight junctions
2) Astrocytes - foot processes wrap around endothelial cells
- Selectively Permeable
- Allows: glucose, fat soluble material to cross
- Not toxins, antibiotics etc
- In most parts of brain except:
Posterior pituitary, hypothalamus, vomiting centre
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Cerebral Arterial Circle
Cerebral arteries form circle at base of forebrain
- Circles pituitary gland and optic chiasma (where optic nerves cross)
- Unites the 2 major blood supplies to the brain (anterior and posterior)
- Provides an alternate toute for blood if vessels blocked
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Blood flow to Brain
Diagram
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Blood Return From The Brain
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Cerebral Arteries
Capillaries
Cerebral Veins
Dural Sinuses
Superior Vena Cava
```
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Cerebrum (Forebrain)
= right and left cerebral hemispheres
- Lobes (named after overlying bones)
1) Frontal
2) Temporal
3) Parietal
4) Occipital
5) Insula - deep to temporal lobe
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Structure Features of the Cerebrum
1) Fissures = deep groves
2) Gyri = ridges
3) Sulci = Shallow Grooves (separate gyri)
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Fissures
1) Longitudinal Fissure
- Separates right and left hemispheres
2) Transverse Fissure
- Separates cerebellum + cerebrum
3) Lateral Fissure
- Separates temporal lobe from rest of cerebrum
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Gyri
Examples:
- Postcentral gyrus in parietal lobe
- Precentral gyrusin frontal lobe
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Sulci
Example:
| - Central sulcus - between frontal and parietal lobes
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Layers to the Cerebrum
1) Cerebral Cortex
2) Tracts (white matter)
3) Basal Nuclei
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Cerebral Cortex
- 2-4 mm thick, grey matter
- Has functional areas:
1) Motor Areas
2) Sensory Areas
3) Association Areas
4) Others
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Motor Areas (Cerebral Cortex)
- All in frontal lobe
- Control skeletal muscle movement
- 3 regions:
1) Primary motor area (pre central gyrus)
2) Premotor Area
3) Broca's - language
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Sensory Areas (Cerebral Cortex)
1) General sensory area (pain, temp, touch, pressure)
- Postcentral gyrus in parietal lobe
2) Vision
- Occipital lobe
3) Auditory + Olfaction
- Temporal lobe
4) Taste + Visceral Sensation (e.g. full bladder)
- Insula
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Association Areas (Cerebral Cortex)
Recognize into from memories - parietal, occipital, temporal lobes
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Others (Cerebral Cortex)
- Memory - Temporal lobes
- Conscious intellect (personality, learning, ideas, judgement etc)
- Prefrontal cortex
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Tracts (white matter)
1) Association Tracts
- Form gyrus to gyrus in same hemisphere
2) Commissural Tracts
- Form gyrus to gyrus in opposite hemispheres
- E.g. corpus callosum
3) Projection Tracts - run vertically (brain to spinal cord/ spinal cord to brain)
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Basal Nuclei
- Paired masses of grey matter (within the white matter)
| - Involved in control of skeletal muscle movement
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Diencephalon
- All gray matter
1) Thalamus
- 2 lobes connected by intermediate mass (bridge of grey matter across 3rd ventricle)
- Relay station for most sensory impulses to cortex
2) Hypothalamus
- Inferior to thalamus, above pituitary
- Major regulator of the internal environment (visceral control)
- e.g. blood pressure, heart rate
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Midbrain
- Connects pons + diencephalon
- Contains cerebral aqueduct
- Anterior portion = cerebral peduncles (projection tracts)
- Posterior portion = 4 nuclei = corpora quadrigemina
~ 2 superior colliculi - visual reflexes
~ 2 inferior colliculi - hearing + auditory reflexes
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Hindbrain
```
Includes:
1) Pons
2) Medulla Oblongata
3) Cerebellum
NOTE: Brain Stem = midbrain, pons, medulla
```
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Pons (Hindbrain)
- Anterior to cerebellum
- Contains:
Tratcs between brain + spinal cord + tracts to/from cerebellum
Pontine respiratory centres
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Medulla Oblongata (Hindbrain)
- Inferior to pons
- Ends at foramen magnum
- 2 bulges called pyramids = large motor tracts (= part of corticospinal tracts)
- Just above spinal cord = decussation of pyramids (tracts cross over)
- 3 vital centres (nuclei) in medulla:
1) Cardiac
2) Vasomotor (blood vessels)
3) Respiratory
- Several non-vital centres - for swallowing, sneezing, vomiting
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Cerebellum (Hindbrain)
- Posterior to pons, medulla
- Has folds similar to gyri = folia - cortex (grey matter(
- Arbor vitae (deep to cortex, anterior cerebellum) = white matter
- Coordinates skeletal muscle contraction - posture, balance
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Limbic System (Functional Systems)
- Nuclei in cerebrum + diencephalon
- Regulates emotions + emotional behaviours (laughing, crying etc)
- Contains areas involved in memory (memories evoke emotional responses)
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Reticular Formation (Functional Systems)
- Nuclei in brain stem
- Cortex, thalamus + hypothalamus involved - together form RAS = Reticular Activating System
- Regulates alertness + attention - filters stimuli + only sends new/unusual signals to other brain areas
- Sleep results when inhibited
- If damaged = coma
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Spinal Cord (Structure Overview)
- Foramen magnum to level of lumbar vertebrae L1?l2 (conus medullar is)
- Nerves continue down from spinal cord through vertebral foramina as caudal equina ("horse's tail") - exit at intervertebral foramina
- Filum terminale
~ CT= extension of Pia mater - anchors conus medullar is of spinal cord to coccyx
~ Location where CSF samples taken
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Spinal Cord (Cross-sectional Structure)
1) Anterior median fissure + posterior median sulcus
2) Central Canal
3) Gray Matter
4) White Matter
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Anterior Median Fissure + Posterior Median Sulcus
- Separate cord into right and left halves
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Central Canal
- Contains CSF
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Gray Matter
- Cell bodies + dendrites of motor neurons, interneurons
- H-shaped
~ Cross bar = gray commissure
~ Horns
1) Dorsal Horn = sensory
2) Lateral Horn = motor
3) Ventral Horn = motor
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White Matter
- Myelinated axons = ascending (sensory) and descending (motor) tracts
- Forms columns:
1) Dorsal Column
2) Lateral Column
3) Ventral Column
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Spinal Cord Function in the CNS
- Carries sensory and motor impulses
| - Produces reflexes - Fas, predictable, automatic responses to changes in the environment (E.g. withdrawal reflex)
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Cranial Nerves (PNS) Pairs)
```
- 12 pairs in total
I. Olfactory
II. Optic
III. Oculomotor
IV. Trochlear
V. Trigeminal
VI. Abducens
VII. Facial
VIII. Vestibulocochlear
IX. Glossopharyngeal
X. Vagus
XI. Accessory
XII. Hypoglassal
```
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Cranial Nerves are associated with the following brain regions:
```
-Forebrain:
Olfactory, Optic
- Midbrain
Oculomotor, Trochlear
- Pons:
Trigeminal, Abducens, Facial, Vestibulocochlear
- Medulla Oblongata
Glossopharyngeal, Vagus, Accessory, Hypoglossal
```
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Cranial Nerves Extra info
1) 2 pairs = only sensory neurons
- I + II
2) 1 pair = mainly sensory
- VIII
3) 9 pairs = mixed nerves
- Carry both sensory + motor neurons
- Motor neurons = cell bodies in brainstem nuclei
- Sensory neurons = cells bodies in ganglia of PNS
- E.g. Trigeminal (V)
Motor function = chewing
Sensory function = conveys general sensations (touch, pressure, pain, temperature etc) from face to CNS
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Spinal Nerves (PNS)
- 31 pairs = all mixed nerves
8 cervical
12 thoracic
5 Lumbar
5 Sacral
1 Coccygeal
- Exit via intervertebral foramina (except 1st - between atlas + occipital bone)
- Each has 2 points of attachment to spinal cord: 1) Dorsal Root and 2) Ventral Root
- Spinal Nerves = joining of dorsal + ventral roots - immediately divides into branches = rami: 1) Dorsal Ramus 2) Ventral Ramus 3) Rami Communicantes
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Dorsal Root
- Sensory; cell bodies in dorsal root ganglion (Have diagram)
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Ventral Root
- Autonomic and somatic motor neurons; cell bodies in ventral or lateral horn
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Dorsal Ramus
Innervates skin + muscles of back
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Ventral Ramus
- Forms thoracic nerves (t2-T12) OR further branch + join up forming nerves plexuses (= nerve networks)
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Rami Communicantes
- Connect ventral ramps to sympathetic trunk
| - Contain autonomic nerve fibres (neurons)
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Cervical Nerve Plexus
- Formed by spinal nerves C1-C5
| - Important nerves arising - Phrenic (innervates diaphragm)
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Brachial Nerve Plexus
- Formed by spinal nerves C5-C8, T1
| - Important nerves arising -Axillary, Radial, Ulnar median, Musculocutaneous
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Lumbar
- Formed by spinal nerves L1-L4
| - Important nerves arising: -Femoral
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Sacral
- Formed by spinal nerves L4-S4
| - Important nerves arising: - Sciatic = divides into tibial + common fibular
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Cross-section of a Nerve (PNS)
1) Nerve = Epineurium - around whole nerve (CT)
2) Axon = Perineurium - around fascicles (CT)
3) Fascicle = Endoneurium - around axon + myelin (CT)
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Peripheral Nervous System: Sensory (Afferent) Division
Consists of:
1) Receptors
a) Location
b) Type of stimulus
c) Structure of Receptor
2) First Order Neurons = sensory neurons
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Receptors of Sensory Division
- Detect changes in environment
- Classified by:
a) Location
b) Type of Stimulus Received
c) Structure of Receptor
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Exteroceptors (Location)
- Stimulus in external environment = receptors at body surface e.g. Touch, most special senses
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Interceptors (Location)
- Stimulus in internal environment (in viscera, blood vessels etc.)
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Proprioceptors (Location)
- Located in joints, skeletal muscles etc.
| - Monitor body position (stretch receptors, muscle spindles) - balance + movement
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Mechanoreceptors (Type of Stimulus Received)
- Mechanical stimuli (e.g. pressure, touch, hearing)
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Thermoreceptors (Type of Stimulus Received)
-Temperature
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Chemoreceptors (Type of Stimulus Received)
- Chemical
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Photoreceptors (Type of Stimulus Received)
- Light
90
Nociceptors
- Pain
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Structure of Receptor (General Senses Only)
1) Free Nerve Endings
- Terminal dendrites of unipolar sensory neurons
- E.g. pain, root hair plexus
2) Encapsulated nerve endings
- Terminal dendrites enclosed in CT
- E.g. Messiner's + Pacinian Corpuscles
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First Order Neurons = Sensory Neurons
- Unipolar neurons attached to or associated with receptor
- Axon located in cranial/ spinal nerves to CNS
- Cell bodies in:
a) sensory ganglia of cranial nerves
b) Dorsal root ganglia of spinal cord
- Axon terminals nuclei
a) Brain nuclei
b) Dorsal horn of spinal cord
