Organisation of the nervous system Flashcards
Nervous system: define central nervous system, peripheral nervous system and autonomic nervous system Regeneration: compare regenerative capacities of injured axons in the central and peripheral nervous systems Afferent vs Efferent: define the terms afferent and efferent as applied to neurons, and recall specific examples of each Circuitry diagrams: draw or interpret simplified circuitry diagrams including spinal cord inputs / outputs, and ascending / descending sensory / motor pathways
What is the nervous system split into?
Central nervous system and peripheral nervous system.
What is the CNS made up of?
Brain, spinal chord.
How is the peripheral nervous system split? (What is each split into?)
Sensory and Motor division (sensory is anything that you sense and goes to your CNS; motor is anything that you respond to and goes from your CNS). Split into SOMATIC sensory/motor DIVISION and AUTONOMIC sensory/motor DIVISION.
What is the somatic and autonomic PNS? (x2 points for each)
Somatic controls motor and sensory function of the BODY WALL e.g. skin (sensory) and skeletal muscle (motor): regulates voluntary movements. Autonomic regulates involuntary movements. Regulates function of the viscera: internal organs, smooth muscle, pupils, sweating, bladder….
What are alternative names for the autonomic nervous system?
Visceral PNS, Vegetative PNS, Involuntary PNS.
What is the autonomic nervous system split into?
Parasympathetic and sympathetic.
Define the sympathetic and parasympathetic nervous systems and their dynamics?
Work in opposite with each other. Sympathetic: stimulate e.g. fight or flight response. Parasympathetic: regulate activities at rest e.g. rest and digest.
What are sensory and motor neurones sometimes re-expressed as? Define each.
Afferent = sensory: anything that goes from the periphery towards the CNS. Efferent = motor: anything that goes from the CNS towards the periphery. AFFERENT = ARRIVE, EFFERENT = EXIT.
What is the structure of a neurone?
Cell body (also called a soma). Dendrites receive signals from other neurones and transmit signals to the cell body. Axon is myelinated and takes signals away from the cell body.
How does synaptic transmission work?
- Action potential comes down to the pre-synaptic terminal. 2. Causes vesicles packed with neurotransmitters to emigrate towards the synaptic cleft. 3. Neurotransmitters released across the cleft. 4. Neurotransmitters bind to receptors on the postsynaptic neurone which initiates an action potential.
Dimension of the synaptic cleft?
Synaptic cleft is 10nm wide.
Differences between regenerative capacity between CNS and PNS? Why is there this difference - mechanisms?
Axons in the PNS can regenerate after injury to some extent. This is because injury in the PNS activates phagocytes which removes debris which would otherwise inhibit growth. Axons in the CNS have limited regenerative capacity. Gila exert inhibitory influence on regeneration. Glial scars form in place of injured tissue. Also because of absence of guidance cues that stimulate axon growth.
What may limit the extent to which PNS is regenerated? (x2)
May be compromised by aberrant axon sprouting (meaning abnormal axon regeneration) and non-specific target reinnervation (meaning restoration of nerve function) – can lead to neuropathic pain.
What does a neural circuit diagram look like?
!!!
What is the mechanism of sensory perception – DORSAL COLUMN-MEDIAL LEMNISCUS PATHWAY (conveys fine tough, vibration and two-point discrimination)?
- Stimulus recognised by sensory receptor. 2. Impulse goes from peripheral area and synapses into grey matter of spinal cord. 3. These cells then send their axons up to the brain stem. 4. At the brain stem, the impulse switches over e.g. if stimulus occurs on left side of the body, the action potential and neuronal route switches to the right side of the brain stem. 5. Impulse continues upwards in another neurone. This neurone goes up to the thalamus (processing centre) which sends inputs to the primary somatosensory cortex (receives all sensory information). This dynamic is called contralateral movement.
What is the mechanism of sensory perception – SPINOTHALAMIC PATHWAY (conveys pain and temperature sensation)?
This pathway is the same as previously outlined but differs because the neuronal pathway switches side as soon as the neurone reaches the spinal cord. NB: THIS DIFFERENCE IS KEY WHEN DIAGNOSING INJURY on different sides of the spinal cord.
What is the mechanism of motor pathways – VESTIBULOSPINAL TRACT (maintain head and eye coordination – balance, dizziness).
The tract receives input from the ears, and efferent neurones cause micro-twitches in the skeletal muscle. The pathway differs from the above motor pathway in being ipsilateral all the way down. This is important because if you are falling in one direction for example, you need to respond to OPPOSE the fall.
CASE 1: Joe is a 72 year-old retired accountant. He has lost voluntary movement and sensation in his left arm, but the muscles still show reflex activity. His right arm and both legs function normally. What areas in the photo do not work.
Affects left side so suggests right side of brain, but only from arm. Voluntary movement is not working which suggests it’s something wrong with nerves in the brain. No injury in peripheral nerves as reflexes not affected because they don’t use the brain. Voluntary movement AND sensation loss suggests both neurones highlighted are affected.
CASE 2: Sophie is a 19 year-old motorcyclist. She has lost voluntary movement and sensation in her left arm. The muscles do not show reflex activity. Her right arm and both legs function normally.
Voluntary movement AND sensation lost but only from one side – but NO reflex activity. (Legs fine) Likely to be a peripheral nerve injury to the left arm/shoulder since there is no reflex activity. Unlikely to be spinal cord as right arm fine
CASE 3: Adam is a 49 year-old taxi-driver. He has lost voluntary movement and sensation in his left arm and leg but the muscles still show reflex activity. His right arm and leg function normally.
If there was no reflex activity, then you can assume that these nerves are affected because the reflex function would not be able to reach the limbs.
