The nervous system Flashcards by Lily Stuart

Describe the brain

Cerebrum
Diencephalon (thalamus and hypothalamus)
Brain stem (midbrain, pons and medulla)
Cerebellum

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Cerebellum

Lies posterior to brain stem
Involved in maintenance of:
- balance
- posture
- muscle tone
Coordinates movement

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Brain stem

Contains ascending and descending nerve fibre tracts
Cranial nerves III - XII arise here
Contains vital centres such as CV and respiratory centres
Contains Midbrain, Pons and Medulla

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Diencephalon

Thalamus:
- important relay station for sensory information
Hypothalamus:
- hormone secretion
- integrating centre for ANS
- thermoregulation
- hunger &amp; satiety centres 
- thirst centre

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Cerebrum

2 hemispheres
Sulci and gyri
Cortex = grey matter
Connecting fibres = white matter
Basal ganglia = grey matter
Hemispheres separated by longitudinal fissure
Organisation:
> Frontal lobe = motor cortex, intellect, mood and social judgement
> Parietal lobe = somatosensory cortex - general sensation and taste
> Temporal lobe = auditory cortex
> Occipital lobe = visual cortex

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The meninges

3 membranes:
- dura mater (top layer)
- arachnoid mater (middle)
- pia mater (inner layer)
Subarachnoid space between pia and arachnoid that contains CSF
CSF secreted into each ventricle of the brain by choroid plexus

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Ventricular system

The ventricles are interconnecting chambers that produce CSF
Lateral ventricles x 2 (cerebral hemispheres)
Third ventricle (lateral walls formed by thalamus)
Cerebral aqueduct (connects 3rd to 4th ventricle)
Fourth ventricle (between brainstem and cerebellum)
Continuous with the subarachnoid space and the central canal of spinal cord

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CSF and its functions

Continuously secreted at a rate of 0.5ml per minute
Supports and protects spinal chord by maintaining pressure =
Acts as shock absorber between brain and skull
Keeps brain and spinal chord moist

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Blood supply to brain

Brain supplied by the internal carotid arteries and vertebral arteries

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Cranial nerves

12 pairs
Arise from brain
May carry:
- only motor fibres
- only sensory fibres
- or both
4 pairs also carry parasympathetic fibres

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Spinal nerves

Supported &amp; protected by vertebral column
Continuous with brain stem
Terminates at the conus medullaris – level L1
31 spinal nerves:
> 8 cervical
> 12 thoracic
> 5 lumbar
> 5 sacral
> 1 coccygeal

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Name a simple non-polarised cell

Kidney cell

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Name a simple polarised cell

Epithelial cells

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Name a highly polarised cell

A neuron

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What are the 2 major cells in the NS?

Glia and Neurons

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Glia

Outnumber neurons in most brain areas
May mediate some signalling in brain
Primary role is to support neurons
Can divide (unlike neurons)
Glia in CNS:
- Oligodendrocytes (myelinated), many axons
- ependymal cells
- astrocytes
Glia in PNS:
- Schwann cells (myelinated) - single axon

Grey matter and white matter

Grey matter = nerve cells bodies, outside of brain and inner part of spinal chord
White matter = axons and myelin, inner part of brain and out part of spinal chord

Resting membrane potential

Inside of neurone is negative (-70mV) compared to outside which is polarised
More sodium outside = positive charge
More potassium and proteins inside = negative charge
This is maintained by sopdium/potassium pump

Action potential

Sodium channels open
Sodium moves into neuron
If impulse reaches threshold (+40mV) = propagation of action potential and depolarisation of axon

Repolarisation

Sodium channels close
Potassium channels open
Potassium moves out
Return of electrical potential to inside negative

Job of myelin

Insulates the axon so electrical impulse is propagated quicker down axon
Multiple Scelerosis is an example of a disease affecting myelin (myelin attacked by own immune system and degraded)

Examples of neurotransmitters at chemical synapses

Serotonin
Acetyl choline	
Glutamate
Dopamine	
GABA		
Noradrenaline	
Adrenaline

CNS control of ANS

ANS information is integrated in hypothalamus

3 neural outputs: somatic, sympathetic, parasympathetic

Sympathetic NS

"fight or flight" response
> tachycardia
> increased BP
> increased blood flow to muscles
> increased blood sugar levels
> inhibits GI peristalsis 
> relaxes airways
> pupil dilation
Control activities that use energy

Parasympathetic NS

``` "rest and digest" response > bradycardia > increased GI motility > bronchial constriction > pupil constriction > gastric acid secretion Control activities that conserve energy ```

Acetylcholine receptors

Neurotransmitter in all preganglionic ANS neurons Parasympathetic ANS postganglionic neurons also release Ach 2 types: > nicotinic receptors (act at ganglionic synapses of sympathetic and parasympathetic divisions) > muscarinic receptors (at target tissues of parasympathetic postganglionic neurons) - muscarinic receptors blocker by ATROPINE - nicotinic receptors blocker by CURARE

Sympathetic NS organisation

``` Acetylcholine and noradrenaline Nicotinic Ach receptors on post-ganglionic neuron Preganglionic neuron = short Location of ganglia = paravertebral Catabolic effects ``` Adrenal medulla: - hormones able to act on sympathetic effector cells Adrenal gland: - stress causes hormones to be released in brain and adrenal gland - cortisol released by adrenal cortex

Stimulant drugs associated with Sympathetic NS

``` Cocaine - stimulant, appetite suppressant - prolongs effects or noradrenaline Amphetamine - psychostimulant - prolongs effects of noradrenaline, dopamine, seretonin ```

Parasympathetic NS organisation

``` Only acetylcholine Nicotinic Ach receptors at post-ganglionic membrane Pre-ganglionic neurone = long Location of ganglia = close to effector Anabolic effects ```

The enteric division

Two complex networks - - myenteric plexus - submucous plexus Controls a lot of processes in food transport and digestion Same number of neurons as whole spinal chord

ANS problems & causes

``` Orthostatic hypotension Inability to sweat/excess sweating Severe constipation Impotence Causes: - diabetes - old age - drugs/medications - autoimmune degradation of nerves - spinal injury - brain tumours ```