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Anatomy > 19 - Nervous System > Flashcards

19 - Nervous System Flashcards

1
Q

What are the two main divisions of the nervous system?

A

1) Central Nervous System (CNS)
- command centre
- brain + spinal cord
- processes + integrates information
2) Peripheral Nervous System (PNS)
- consists of:
a) cranial nerves
to/ from brain
b) spinal nerves
to/ from spinal cord

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2
Q

What are the two divisions of the PNS?

A

a) sensory/afferent division
- has sensory receptors that detect stimuli (changes in the internal or external environments
- nerves convey impulses toward CNS
b) motor/efferent division
- nerves convey impulses away from CNS
- innervates (supplies nerves to) effectors = muscles + glands (endocrine or exocrine)

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3
Q

Describe Neurons

A
  • conduct impulses
  • make up CNS + PNS
  • mostly amitotic (irreplaceable)
    exceptions = taste, olfaction, memory
  • structure:
    a) cell body
    • typical organelles
    • RER called Nissl bodies
    • groups/clusters in CNS = nuclei (gray matter)
    • groups/clusters in PNS = ganglia
      b) processes from cell body:
      i) dendrites
      • receive incoming messages + relay to cell body
        ii) axon
        • carries impulses away from cell body
      • axon hillock - where axon meets cell body
      • axon terminal → typically branched with synaptic end bulbs (enlarged tips)
      • may be:
        ① 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:
        - CNS = tracts (white matter)
        • PNS = nerves
          ② unmyelinated - no myelin
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4
Q

Describe the types of Neuroglia

A
  • support neurons = can undergo mitosis (prone to cancer – brain tumour)
  • types:
    a) CNS neuroglia
    i) oligodendrocytes
    - produce myelin around axon
    ii) microglia
    - protective ⇒ become phagocytic if detect infected, dead or damaged neurons (because immune cells can’t enter CNS)
    iii) astrocytes
    - surround blood capillaries to form part of blood brain barrier (BBB)
    - help control capillary permeability
    iv) ependymal cells - neural epithelium
    - line brain ventricles + central canal of spinal cord
    - secrete cerebrospinal fluid (CSF) + circulate it (cilia)

b) PNS neuroglia
i) Schwann cells
- form myelin around axons in PNS
ii) Satellite cells
- surround neuron cells bodies in ganglia
- protection and support

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5
Q

What are the structural/anatomical classifications of neurons?

A
  • based on number of processes coming off cell body
    a) unipolar
    • 1 process that divides into two: central + peripheral
    • peripheral end has dendrites = sensory receptors (pain, touch etc) - remainder is axon
    • always sensory
      b) bipolar
    • 2 processes: 1 axon, 1 process with dendrites
    • sensory ⇒ retina, nose (olfaction
      c) multipolar
    • 3 or more processes: 1 axon, many dendrites
    • all interneurons + motor neurons
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6
Q

What are the functional classifications of neurons?

A
  • based on direction of impulse conduction
    a) Sensory/Afferent neurons
    • mostly unipolar
    • from sensory receptors to CNS
      b) Interneurons
    • within CNS (between sensory + motor)
    • 99% of neurons (mostly multipolar)
      c) Motor/Efferent neurons
    • CNS to effectors (all multipolar)
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7
Q

What are the types of synapses

A

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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8
Q

Describe chemical neural synapses

A
  • most common
  • structure:
    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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9
Q

What are the meninges?

A
  • CT around brain + spinal cord
  • layers:
    a) 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
      b) 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)
    • project into dural sinuses
    • CSF enters villi to return to blood
      c) Pia mater (inner)
    • on surface of CNS (brain and spinal cord)
    • vascular
  • meningitis = inflammation of meninges
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10
Q

Describe CSF

A

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
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11
Q

Describe the circulation of CSF

A 
1st and 2nd Ventricle
Interventricular foramina
3rd ventricle
cerebral aqueduct
4th ventricle
median (1) and lateral (2) apertures
subarachnoid space
arachnoid vila
dural sinus
interjugular veins
heart
arterial blood
choroid plexuses
all ventricles
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12
Q

Describe the BBB

A

Blood-Brain Barrier (BBB):

  • 2 cell types:
    a) endothelial cells (of capillaries) with tight junctions
    b) 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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13
Q

Describe the cerebral arterial circle

A
  • 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 route for blood if vessels blocked

blood flow to the brain:
Posteriorly:
Vertebral Arteries -> Basilar Arteries -> Posterior Cerebral Arteries

Anteriorly:
Internal Carotid Arteries 
 ->Middle cerebral arteries
 ->*Posterior Communicating Artery*
 ->*Anterior Cerebral Arteries* -> *Anterior Communicating Artery*
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14
Q

Describe the blood return from the brain

A 
Cerebral Arteries
Capillaries
Cerebral Veins
Dural Sinuses
Superior Vena Cava
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15
Q

What are the three parts of the brain?

A

Forebrain
Midbrain
Hindbrain

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16
Q

What are the parts of the forebrain?

A

Cerebrum

Diencephalon

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17
Q

What are the lobes of the cerebrum?

A

(= right and left cerebral hemispheres)

  • lobes (named after overlying bones)
    i) frontal
    ii) temporal
    iii) parietal
    iv) occipital
    v) insula – deep to temporal lobe
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18
Q

What are the surface features of the cerebrum?

A

i) fissures = deep grooves
① longitudinal fissure
- separates right and left hemispheres
② transverse fissure
- separates cerebellum + cerebrum
③ lateral fissure
– separates temporal lobe from rest of cerebrum
ii) gyri = ridges
- examples:
- postcentral gyrus in parietal lobe
- precentral gyrus in frontal lobe
iii) sulci = shallow grooves (separate gyri)
- example:
- central sulcus – between frontal and parietal lobes

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19
Q

What are the three layers of the cerebrum?

A

Cerebral Cortex
Tracts
Basal Nuclei

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20
Q

Describe the cerebral cortex

A
  • 2-4 mm thick, gray matter
  • has functional areas:
    ① motor areas
    • all in frontal lobe
    • control skeletal muscle movement
    • 3 regions:
      a) primary motor area (precentral gyrus)
      b) premotor area
      c) Broca’s – language
      ② sensory areas
      a) general sensory area (pain, temp, touch, pressure)
      • postcentral gyrus in parietal lobe
        b) vision
        – occipital lobe
        c) auditory + olfaction
      • temporal lobe
        d) taste + visceral sensation (e.g. full bladder) - insula
        ③ association areas
  • recognize info from memories
    • parietal, occipital, temporal lobes
      ④ others
  • memory
    - temporal lobes
  • conscious intellect (personality, learning, ideas, judgement etc)
    • prefrontal cortex
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21
Q

Describe the tracts of the cerebrum

A
  • types:
    ① association tracts
    • from gyrus to gyrus in same hemisphere
      ② commissural tracts
    • from 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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22
Q

Describe the basal nuclei

A
  • paired masses of gray matter (within the white matter)

- involved in control of skeletal muscle movement

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23
Q

Describe the diencephelon

A
  • all gray matter
    i) thalamus
    • 2 lobes connected by intermediate mass (bridge of gray matter across 3rd ventricle)
    • relay station for most sensory impulses to cortex
      ii) hypothalamus
    • inferior to thalamus, above pituitary
    • major regulator of the internal environment (visceral control)
      e. g. blood pressure, heart rate
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24
Q

Describe the Midbrain

A
  • 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
25
Q

What are the three parts of the hindbrain

A

pons
medulla oblongata
cerebellum

26
Q

Describe the pons

A
  • anterior to cerebellum
  • contains
    • tracts between brain + spinal cord + tracts to/from cerebellum
    • pontine respiratory centres
27
Q

Describe the medulla oblongata

A
  • 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:
    i) cardiac
    ii) vasomotor (blood vessels)
    iii) respiratory
  • several non-vital centres - for swallowing, sneezing, vomiting
28
Q

What is the brain stem?

A

Brain Stem = midbrain, pons, medulla

29
Q

Describe the cerebellum

A
  • posterior to pons, medulla
  • has folds similar to gyri = folia
    • cortex (gray matter)
  • arbor vitae (deep to cortex, anterior cerebellum) = white matter
  • coordinates skeletal muscle contraction
    • posture, balance
30
Q

What are the two functional systems of the brain

A

Limbic system

Reticular Formation

31
Q

Describe the limbic system

A
  • nuclei in cerebrum + diencephalon
  • regulates emotions + emotional behaviours (laughing, crying etc)
  • contains areas involved in memory (memories evoke emotional responses)
32
Q

Describe the reticular system

A
  • nuclei in brain stem
  • cortex, thalamus + hypothalamus involved
  • together form RAS = Reticular Activating System
  • regulates alertness + attention
  • filtres stimuli + only sends new/unusual signals to other brain areas
  • sleep results when inhibited
  • if damaged = coma
33
Q

Describe the general structure of the spinal cord

A
  • foramen magnum to level of lumbar vertebrae L1/L2 (conus medullaris)
  • nerves continue down from spinal cord through vertebral foramina as cauda equina (“horse’s tail”)
    • exit at intervertebral foramina
  • filum terminale
    • CT = extension of pia mater - anchors conus medullaris of spinal cord to coccyx
    • location where CSF samples taken
34
Q

Describe the cross section of the spinal cord

A 
a) anterior median fissure + posterior median sulcus
Separate cord into right and left halves
b) central canal 
	– contains CSF
c) gray matter
	- cell bodies + dendrites of motor neurons, interneurons
	- H-shaped
	- cross bar = gray commissure
	- horns
		i) dorsal horn = sensory
		ii) lateral horn = motor
		iii) ventral horn = motor	
d) White matter
	- myelinated axons = ascending (sensory) and descending (motor) tracts
	- forms columns:
		i) dorsal column
		ii) lateral column
		iii) ventral column
35
Q

What are the functions of the spinal cord

A
  • carries sensory and motor impulses
  • produces reflexes
    • fast, predictable, automatic responses to changes in the environment
      e. g. withdrawal reflex
36
Q

What are the twelve cranial nerve pairs?

A
  1. Olfactory
  2. Optic
  3. Oculomotor
  4. Trochlear
  5. Trigeminal
  6. Abducens
  7. Facial
  8. Vestibulochochlear
  9. Glossopharyngeal
  10. Vagus
  11. Accessory
  12. Hypoglossal

(Oh once one takes the anatomy final very good vacations are had)

37
Q

Which brain regions are the cranial nerve pairs associated with?

A

Forebrain: 1,2
Midbrain: 3,4
Pons: 5,6,7,8
Medulla Oblongata: 9, 10, 11, 12

38
Q

Which pairs of cranial nerves are only sensory? Mainly sensory? What are the rest?

A

Only sensory: 1,2
Mainly sensory: 8
Rest: sensory and motor

39
Q

Where are the cell bodies of the cranial nerves?

A
  • motor neurons ⇒ cell bodies in brainstem nuclei

- sensory neurons ⇒ cell bodies in ganglia of PNS

40
Q

What does the Trigeminal nerve do?

A
  • motor function = chewing

- sensory function = conveys general sensations (touch, pressure, pain, temperature etc) from face to CNS

41
Q

Where do the spinal nerves come out?

A
  • 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)
42
Q

Describe the structure of a spinal nerve

A
  • each has 2 points of attachment to spinal cord:
    a) Dorsal Root
    • sensory; cell bodies in dorsal root ganglion
      b) Ventral Root
    • autonomic and somatic motor neurons; cell bodies in ventral or lateral horn
    • spinal nerve = joining of dorsal + ventral roots
    • immediately divides into branches = rami:
      a) dorsal ramus
      innervates skin + muscles of back
      b) ventral ramus
      - forms thoracic nerves (T2 - T12) OR further branch + join up forming nerves plexuses (= nerve networks)
      c) rami communicantes
    • connect ventral ramus to sympathetic trunk
    • contain autonomic nerve fibres (neurons)
43
Q

What are the spinal nerve plexuses

A

1) Cervical: C1 - C5 {phrenic (innervates diaphragm)}
2) Brachial: C5 - C8, T1 {axillary, radial, ulnar, median, musculocutaneous}
3) Lumbar: L1 - L4 {femoral}
4) Sacral: L4 - S4 {sciatic ⇒ divides into tibial + common fibular}

44
Q

Describe the cross section of a nerve

A 
nerve
axon
fascicle
epineurium - around whole nerve (CT)
perineurium - around fascicles (CT)
endoneurium - around axon + myelin (CT)
45
Q

What are the classifications of receptors in the sensory division?

A

location
stimulus
structure

46
Q

Describe the locational classification of sensory receptors

A

a) location
i) exteroceptors
- stimulus in external environment = receptors at body surface e.g. touch, most special senses)
ii) interoceptors
- stimulus in internal environment (in viscera, blood vessels etc)
iii) proprioceptors
- located in joints, skeletal muscles etc
- monitor body position (stretch receptors, muscle spindles) – balance + movement

47
Q

Describe the stimulus classifications of sensory receptors

A

i) mechanoreceptors
- mechanical stimuli (e.g. pressure, touch, hearing)
ii) thermoreceptors
- temperature
iii) chemoreceptors
- chemical
iv) photoreceptors
- light
v) nociceptors
- pain

48
Q

Describe the structural classifications of sensory receptors

A

i) free nerve endings
- terminal dendrites of unipolar sensory neurons e.g. pain, root hair plexus
ii) encapsulated nerve endings
- terminal dendrites enclosed in CT
e. g. Meissner’s + Pacinian corpuscles

49
Q

Describe first order neurons

A
  • 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 in:
    a) brain nuclei
    b) dorsal horn of spinal cord
50
Q

What are the two divisions of the motor division of the nervous system

A

Somatic

Autonomic

51
Q

Describe the somatic motor division

A
  • effector = skeletal muscle
  • consists of lower motor neurons:
    = single multipolar neuron:
    a) cell body in ventral horn of spinal cord to effector
    b) cell body in motor nuclei of brain stem to effector (e.g. facial motor nucleus for cranial nerve VII)
52
Q

Describe the autonomic motor division

A
  • effector = smooth muscle, cardiac muscle, glands
  • 2 successive multipolar neurons from CNS to effector:
    a) preganglionic neuron
    • myelinated
    • cell body in brain stem or lateral horn of spinal cord
      b) postganglionic neuron
    • unmyelinated
    • cell body in autonomic ganglion (outside CNS)
  • 2 subdivisions:
    a) Sympathetic (SNS)
    b) Parasympathetic (PSNS)
53
Q

Describe the SNS

A

Cell body of the preganglionic neuron is in the lateral horn (T1-L2)
Autonomic ganglia are in the trunk (either side of the vertebral column) or collateral (anterior to vertebral column or close to large abdominal arteries)
Postganglionic neurons have long axons
It’s function is the fight or flight response
It exits the CNS as mainly thoracic nerves
The adrenal medulla is modified postganglionic neurons of the SNS

54
Q

Describe the PSNS

A

Cell body of the preganglionic neuron is in the brain stem S2-S4
Autonomic ganglia are terminal (at or in organ or effector)
Postganglionic neurons have short axons
It’s function is rest and digest
It exits the CNS as mainly (80%) vagus nerve

55
Q

Describe the neurons of the ascending pathway.

A
  • conducts impulses from general sense receptors into brain
  • 3 successive neurons from receptor to cortex:
    a) First Order Neuron
    - receptor to spinal cord (PNS)
    b) Second Order Neuron
    • interneuron, multipolar (CNS)
    • cell body in dorsal horn of spinal cord or medulla (CNS)
    • decussates (crosses over) in spinal cord or medulla
      c) Third Order Neuron
    • interneuron, multipolar
    • cell body in thalamus – impulses to postcentral gyrus (sensory cortex) (CNS)
56
Q

Describe the tracts of the ascending pathway.

A
  • axons of 1st or 2nd order neurons form ascending spinal tracts:
    a) Posterior (Dorsal) Column Pathway /Tracts
    • sensations can be precisely located (touch)
    • receptors = free nerve endings, Meissner’s etc
      b) Spinothalamic Pathway/Tracts
    • non-specific, difficult to localize
    • receptors = temperature, pain
      c) Spinocerebellar Pathway/Tracts
    • ascending tracts from spinal cord to cerebellum
    • receptors = proprioceptors
    • 2nd order neuron directly to cerebellum (no 3rd order)
    • no conscious perception
    • no decussation
57
Q

Describe the neurons of the descending pathway

A
  • conduct impulses from brain to effector
  • 2 neuron pathway:
    a) Upper Motor Neuron (CNS):
    • multipolar interneurons
    • cell bodies in cortex or brainstem nuclei
      b) Lower Motor Neuron (cell bodies in ventral horn (CNS) and axons in PNS)
58
Q

Describe the tracts of the descending pathway

A
  • axons of upper motor neurons form descending spinal tracts:
    a) Corticospinal Tracts:
    • cell bodies in cerebral cortex
    • tracts mainly decussate in medulla
      b) Indirect Tracts
    • cell bodies in brainstem nuclei
    • receive impulses from motor cortex, basal nuclei, cerebellum

Anatomy (20 decks)

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