The nervous system Flashcards
Describe the brain
Cerebrum
Diencephalon (thalamus and hypothalamus)
Brain stem (midbrain, pons and medulla)
Cerebellum
Cerebellum
Lies posterior to brain stem Involved in maintenance of: - balance - posture - muscle tone Coordinates movement
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
Diencephalon
Thalamus: - important relay station for sensory information Hypothalamus: - hormone secretion - integrating centre for ANS - thermoregulation - hunger & satiety centres - thirst centre
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
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
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
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
Blood supply to brain
Brain supplied by the internal carotid arteries and vertebral arteries
Cranial nerves
12 pairs Arise from brain May carry: - only motor fibres - only sensory fibres - or both 4 pairs also carry parasympathetic fibres
Spinal nerves
Supported & 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
Name a simple non-polarised cell
Kidney cell
Name a simple polarised cell
Epithelial cells
Name a highly polarised cell
A neuron
What are the 2 major cells in the NS?
Glia and Neurons
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
