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Biomedicine II > 14. Nervous System II > Flashcards

14. Nervous System II Flashcards

1
Q

Central Nervous System

A

The central nervous system (CNS)

consists of the brain and spinal cord.

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2
Q

Spinal Cord

A

Protected by the vertebral column & meninges.

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3
Q

Brain

A

Protected by the cranium, cranial meninges, cerebrospinal fluid (CSF) & the
blood brain barrier (BBB).

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4
Q

Meninges

A

Three layers of connective tissue that cover the brain & spinal cord:
Dura Mater
Arachnoid Mater
Pia Mater

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5
Q

Dura Mater

A

The tough outer layer divides into 2 layers in the brain to create venous sinuses that allow blood to drain out of the brain into the jugular veins.

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6
Q

Arachnid Mater

A
  • Collagen and elastic fibres.

* Subdural space between arachnoid mater and dura mater filled with interstitial fluid.

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7
Q

Pia Mater

A
  • Thin transparent layer that contains blood vessels that supply the spinal cord.
  • Between the pia mater and arachnoid mater is the sub arachnoid space filled with cerebrospinal fluid.
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8
Q

Haemorrhages

A

Subdural haematoma

Subarachnoid haemorrhage

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9
Q

Subdural haematoma

A

Venous bleed (slowly develops).

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10
Q

Subarachnoid haemorrhage

A

Arterial bleed (rapid).

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11
Q

Cerebrospinal Fluid (CSF)

A

• CSF is a clear liquid that protects the brain & spinal cord from mechanical and
immunological trauma.
•It is made from filtered blood & is mostly water with ions & glucose. Blood cells are too large to filter through, making CSF colourless.
• CSF occupies the subarachnoid space &
the ventricles (cavities) in the brain, as well as the central canal of the spinal cord.
• Produced by ependymal cells continuously at a rate of 500 ml/day . However, the brain can only contain about 150 ml, so large amounts are gradually absorbed back into the blood.

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12
Q

Cerebrospinal Fluid (CSF): Functions

A
  • Supports & protects the brain and spinal cord, acting as a shock absorber.
  • Maintains uniform pressure around the brain in case of brain enlargement compensation occurs by reduction of CSF.
  • Keeps brain & spinal cord moist.
  • Circulates nutrients and waste.
  • Optimal chemical environment for nerve signalling i.e. ions.
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13
Q

Blood Brain Barrier (BBB)

A

• Blood flows to the brain from the vertebral and carotid arteries.
• Brain uses 20% of the body’s oxygen and glucose at rest neurons die within minutes of being deprived of oxygen.
• The BBB protects the brain from toxins,
harmful substances and bacteria that enter the bloodstream by maintaining tightness of the capillaries and the junctions between cells.
• The BBB is maintained by ‘astrocytes’.

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14
Q

Transport across the BBB

A
  • Lipid soluble substances cross easily e.g. alcohol, anaesthetics.
  • Glucose crosses by active transport.
  • Gases diffuse easily e.g. oxygen, carbon dioxide.
  • Ions diffuse slowly across.
  • Proteins and some drugs do not pass.
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15
Q

The Brain

A
  1. Brainstem:
    • Divided into the medulla oblongata, pons & midbrain.
  2. Diencephalon (‘ interbrain’):
    • Divided into thalamus, hypothalamus & epithalamus
  3. Cerebrum.
  4. Cerebellum (‘little brain’).
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16
Q

Brainstem

A

• The brainstem is a continuation of the spinal cord in the cranium (beyond the ‘foramen magnum’).
Medulla oblongata
Pons
Midbrain

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17
Q

Diencephalon

A

Thalamus
Hypothalamus
Epithalamus

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18
Q

Medulla oblongata

A
  • Contains the respiratory and cardiac centres (regulates heartbeat & breathing). • Controls reflexes such as vomiting, sneezing & hiccupping.
  • Contains four cranial nerves ( 9-12)
  • Contains motor tracts (corticospinal tract).
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19
Q

Pons

A
  • Helps to control breathing.
  • Four pairs of cranial nerves (5-8)
  • Relays motor tracts.
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20
Q

Midbrain

A 
• Contains the ‘substantia nigra’ (large,
darkly pigmented area that contains
dopamine releasing neurons that help
control subconscious muscle activities
• Eye reflexes and tracking.
• Two cranial nerves (3 & 4).
• Auditory tracts.
• Movement of head and neck.
• Transfers motor tracts.
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21
Q

Thalamus

A 
• The core of the brain, making up 80%
of the diencephalon.
• ‘Major relay centre’ relays sensory
information to the cerebrum.
• Integrates sensory and motor information.
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22
Q

Epithalamus

A

• Connects limbic system to other
parts of the brain.
• Contains the pineal gland which
secretes melatonin.

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23
Q

Hypothalamus

A 
• Hormone regulation and homeostasis.
• Receives sensory information (i.e. from
viscera, smell).
• Controls the ANS (a major regulator of
visceral activities).
• Controls body temperature.
• Regulates emotional and behavioural
patterns (limbic), eating & drinking
(appetite/satiety) & regulation of circadian
24
Q

Cerebellum

A

• Located in the inferior and posterior
aspect of the cranium.
• Of the 100 billion neurons in the brain, half of them are packed into the cerebellum, despite it only accounting for 1/10 th of brain mass.

25
Q

Cerebellum: Fucntions

A

• Maintenance of posture and balance.
• Functions to co ordinate and smooth complex (‘skilled’) sequences of movements.
• Correction of errors during on going movement.
Discrepancies are detected by cerebellum and sends feedback to cerebrum via the thalamus.
• E .g. learning to walk, learning an instrument.
• Also thought to play a role in cognition, thought and language processing.
• It alters motor behaviour by altering circuits that influence motor pathways (corticospinal tracts).
• The cerebellum is susceptible to injury from chronic alcohol abuse . Cerebellar damage may also result from coeliac disease or a thiamine (vitamin B1)
• Cerebellar disease produces symptoms of ‘ataxia’: lack of muscle co ordination. Commonly results in stumbling, unsteadiness, slurred speech
and an intention tremor (e.g. hand tremor when putting key in door).

26
Q

The Cerebrum

A
  • The cerebrum is divided into two hemispheres (left & right
  • The cerebrum contains an outer cerebral cortex that contains grey matter . It has multiple folding’s (fissures).
  • The cerebrum has a deeper region of cerebral white matter
  • The two cerebral hemispheres are connected by the ‘corpus callosum’, allowing coordination of movements between sides (e.g. walking)
  • The brain does not decide what a person does. The individual uses the brain like a computer!
27
Q

The Cerebrum: Functions

A
  • Sensory perception.

* Motor control of skeletal muscles (movement).

28
Q

Cerebrak Hemispheres

A

• Motor neuron axons join to form the corticospinal tract. These motor tracts cross over in the medulla oblongata (decussating).
• This means the left side of the brain co-ordinates the right side of the body
• The right side of the brain co-ordinates
the left side of the body.

29
Q

The Cerebrum Structure

A

• Each cerebral hemisphere can be further
subdivided into four lobes, which are named after the bones that cover them:
• Frontal, parietal, temporal, occipital.
• Each of these lobes performs different
functions:

30
Q

Frontal Lobe

A

The frontal lobe is involved in motor

skills.

31
Q

Temporal Lobe

A

The temporal lobe is involved in hearing.

32
Q

Parietal Lobe

A

The parietal lobe contains the sensory cortex.

33
Q

Occipital Lobe

A

The occipital lobe plays a role in vision.

34
Q

The Limbic System

A

• The limbic system is area of the brain that is active with different emotions but again, remember this does not control your emotions (you do).
• The limbic system is formed of several functionally and anatomically interconnected structures including parts
of the cerebrum, diencephalon and midbrain.
• Key structures within the limbic system include the hypothalamus, hippocampus & amygdala.
• The limbic system becomes active when dealing with emotional responses to our environments.
• The amygdala is a key area in ‘emotions’ whilst the hippocampus plays an essential role in encoding and retrieving memories.

35
Q

Brain Blood Supply

A

• The brain has a very limited ability to store oxygen or glucose, therefore a constant supply is necessary.
• Brain receives about 20% of cardiac
output (about 750ml per minute), despite accounting for 2% of body mass.
• Cardiovascular health is important for
brain health.
• The blood supply to the brain is from two
major arterial systems: carotid & vertebral.
• The two arterial systems meet to form the
‘Circle of Willis’. This is a common location
for aneurysms to develop: “berry aneurysms”.

36
Q

Cranial Nerve I

A

Ofactory - sense of smell

37
Q

Cranial Nerve II

A

Optic - vision

38
Q

Cranial Nerve III

A

Oculomotor - eye movements, eyelid opening, pupil size

39
Q

Cranial Nerve IV

A

Trochlear - eye movements

40
Q

Cranial Nerve V

A

Trigeminal - facial sensations, chewing

• CN V has 3 branches: Ophthalmic, maxillary and mandibular.

41
Q

Cranial Nerve VI

A

Abducens - Eye Movement (abducts eye)

• Damage to CN III, IV, VI can lead to strabismus (one eye crossed), ptosis (drooping of upper eyelid) & diplopia (double

42
Q

Cranial Nerve VII

A

Facial - Taste, facial expressions, salivary glands

43
Q

Cranial Nerve VIII

A

Vestibulocochlear - Hearing, balance

44
Q

Cranial Nerve IX

A

Glossopharyngeal - taste, swallowing, tongue sensations

45
Q

Cranial Nerve X

A

Vagus - Sensory and motor functions in chest and abdomen
• ALL sensory information from the chest and abdomen (Heart, GI tract, lungs) e.g.
Sensation from epiglottis, detects gas levels in arteries.
• The largest nerve of the autonomic NS
mostly parasympathetic but some sympathetic (Increased BP).
• Both sensory & motor function but 90% of
fibres are afferent (sensory).
• Injuries may result in tachycardia, dysphagia. Vaso vagal syncope (fainting).

46
Q

Cranial Nerve XI

A

Accessory - Neck and shoulder movement

47
Q

Cranial Nerve XII

A

Hypoglossal - Tongue mvoement and speech

48
Q

Spinal Cord

A

• The spinal cord begins at the foramen magnum and terminates at the vertebral
level L2 as the ‘conus’.
• The meninges continue beyond L2 to the level of S2 (sacrum).
• The ‘cauda equina’ (“horses tail”) consists of spinal nerves that continue beyond the conus.

49
Q

Spinal Cord Physiology

A

• The spinal cord consists of white

matter around a core of grey matter.

50
Q

White Matter

A 
• Consists of bundles of myelinated
axons.
Made up of ‘ tracts’ (“highways):
1. Motor (descending) tracts :
Voluntary & involuntary movement
(coordination, posture, balance).
2. Sensory (ascending) tracts
Transmit impulses from skin, tendons, muscles & joints (e.g. touch, vibration, proprioception).
51
Q

Grey Matter

A 
• Consists of cell bodies & dendrites.
Receives and integrates incoming and outgoing information. Divided into:
1. Posterior (Dorsal) Horn:
Receives sensory impulses.
2. Anterior (Ventral) Horn:
Sends out motor impulses.
52
Q

Spinal Cord Tracts

A
  1. Dorsal columns
  2. Spinothalmic tract
  3. Corticospinal Tract
    • Damage to any of the spinal tracts would
    lead to loss of the tracts function below
    that level in the body.
53
Q

Dorsal Columns

A

Ascending Tract

Light Touch, vibration, proprioception

54
Q

Spinothalmic tract

A

Ascending Tract

Pain and temperature

55
Q

Corticospinal tract

A

Descending tract

Voluntary movements

56
Q

Reflex Arcs

A 
• A reflex is a fast, automatic, unplanned sequence of actions that occurs in response to a stimulus.
• If the integration takes place in the
spine it is known as a ‘ spinal reflex’.
1. Sensory receptor
2. Sensory neuron
3. Integrating centre (interneuron)
4. Motor neuron
5. Effector organ
57
Q

Spinal Nerves

A 
• The spinal cord contains extensions
called ‘spinal nerves’, which exit the vertebral column through holes in
the vertebra called vertebral foramina
(holes).
• Each spinal nerve corresponds with a
vertebral foramina.

Biomedicine II (16 decks)

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