Physiology condensed Flashcards
Parts of the neurone?
Dendrites
Cell body (soma)
Cell membrane
Nucleus
Axon hillock
Myelin sheath
Node of Ranvier
Schwann cell
Axon
Axon terminal
Dendrite function?
Receives the signals from other cells
Cell body function?
Organises and keeps the cell functional
Cell membrane function?
Protects the cell
Axon hillock function?
Generates impulses in the neurone
Node of Ranvier function?
Allows the diffusion of ions
Schwann cell function?
Produces the myelin sheath. Particularly in the PNS
Axon terminal function?
Forms junctions with other cells
Myelin sheath function?
Increases speed of signal
Axon function?
Transfers signals to other cells and organs
Nucleus function?
Controls the entire neurone
How many neurone types are there and what are they?
4 types:
Unipolar
Pseudounipolar
Bipolar
Multipolar
All pseudounipolar neurones are sensory. True/false?
True
Unipolar neurones are present in humans. True/false
False, only present in invertebrates i.e. flies etc.
Bipolar neurone primary function?
Mainly used as special sense neurones used for the transmission of sense.
Multipolar neurones primary function?
Function is to conduct motor impulses within the brain and spinal cord. These are the most abundant neurone type in the brain.
Stages of action potential?
1) Initiating depolarisation as a result of a stimulus.
2) Depolarisation curve. During this, Na+ ion influx.
3) At the peak of the curve, Na+ ion channels begin to close and K+ ion channels begin to open.
4) Repolarisation curve. During this, K+ ion efflux.
5) When getting back down to threshold. K+ ion channels begin to close.
6) In hyperpolarisation, all K+ leak channels open and some V gated K + channels still open.
7) All channels close upon reaching resting state.
The order of the somatosensory system?
1) Stimulus
2) Cation channels (channels that allow flow of both Na and K ions) -> depolarising potential.
Higher amplitude = higher stimulus intensity.
3) If amplitude > threshold. A.P is at a frequency proportional to amplitude.
4) Action potential (A.P) arriving at the central terminal causes the realease of neurotransmitter to the 2nd neuron.
Low threshold units = ?
Low intensity, non-damaging stimulus. Examples include fine discriminatory touch.
High threshold units (nociceptors) = ?
High intensity, damaging stimulus. Examples include:
High intensity mechanical stimuli.
Thermal nociceptors - respond to temp extremes (<10, >45).
Chemical nociceptors - repond to substances in tissues (inflammation).
Types of skin sensory receptors?
Free nerve endings
Meissner’s corpuscles
Merkel’s discs
Pacinian corpuscles
Krause end bulbs
Ruffini ending’s
What are free nerve endings?
Present in the skin and can detect temperature and mechanical stimuli such as pain, itch, pressure or stretch.
What are Meissner’s corpuscles?
Responsible for detecting vibrations on the skin.
What are Pacinian corpuscles?
Responsible for detecting pressure on the skin.
What are Merkel’s discs?
Responsible for detecting light touch on the surface of the skin.
What are krause end bulbs?
Detect cold on skin surface
What are Ruffini’s endings?
Detect warmth on skin surface
What does the motor system consist of?
Upper motor neurons (UMN) - in brain
Lower motor neurons (LMN) with soma - brain stem and ventral horn of spinal cord.
What do the LMN’s consist of?
Alpha motor neurons - innervate extrafusal muscle fibres.
Gamma motor neurons - innervate muscle spindles (intrafusal muscles fibres).
What is a motor unit definition?
Alpha motor neurone + all the skeletal muscle fibres innervated.
What is a motor neurone pool?
A collection of alpha motor nuerones that innervate a single muscle.
What is muscle strength influenced by?
Activation of muscle fibres (firing rate of LMN’s involved, number of LMN’s contributing to force).
Force production by muscle fibres
- Fibre size (hypertrophy)
- Fibre phenotypes (fast or slow)
A single action potential in an alpha motor neurone causes a muscle to twitch. True/false?
True
Deep tendon reflexes?
Biceps (elbow) : C5, C6
Quadriceps (knee) : L3, L4
Gastrocnemius (ankle) S1, S2
What are extrafusal muscle fibres?
Comprises the bulk of the muscle and forms the major force-generating structure.
What are intrafusal muscle fibres?
Buried in the muscle, containing afferent receptors for stretch but also contain contractile elements.
Another name from myotatic reflex?
Stretch reflex
What activates myotatic reflex?
Activated by stretch of sensory muscle spindle.
Of the lateral pathways. What is the major pathway?
Corticospinal (pyramidal) tract
Of the lateral pathway. What is the minor pathway?
Rubrospinal tract
Sequence of events for corticospinal (pyramidal) tract?
1) Cell bodies form motor cortex and somatosensory areas of parietal cortex.
2) Axons go down a pyramid - like structure towards base of medulla.
3) After medulla, 85% fibres cross at the pyramidal decussation (intersection of 2 or more objects) to form:
- Lateral corticospinal tract
- Remainder stay ipsilateral (occurring same side of body) to form ventral (anterior) corticospinal tract
4) Axons then terminate at dorsolateral region of ventral horn.
Sequence of events for rubrospinal tract?
1) Cell bodies located in red nucleus which receive input from motor cortex and cerebellum.
2) Axons decussate at the ventral tegmental decussation and descend lateral to ventralolateral corticospinal tract.
3) Terminates at ventral horn (anterior horn) of grey matter and has control over limb flexor muscle.
Rubrospinal tract cannot compensate for a damaged corticospinal tract. True/false?
False. damaged corticospinal tract can be compensated with rubrospinal tract.
Lesions of the corticospinal tracts are associated with what symptoms?
- Loss of “fractionated” movements (elbows, wrists, fingers can’t move independently)
- Slowing and impairment of accuracy of voluntary movements.
- Little effect on normal posture.
Lesions of corticospinal tract tend to recover over time. True/false?
True
Process of hair cell transduction?
- Tectorial membrane vibrates
- Hair cells’ cilia bend
- Release of neurotransmitter
- Released neurotransmitter captured in nerve fibres
What do the semi-circular canals do?
Sense head angular acceleration (rotation).
What are the 3 types of pain?
Nociceptive - adaptive
Inflammatory - adaptive
Pathological - maladaptive
What are nociceptors?
Peripheral sensory afferent neurones, activated by intense noxious stimuli. They are first order neurones that relay info to 2nd order neurones in the CNS.
2 types of nociceptors?
Alpha fibres - mechanical/thermal nociceptors that are thinly myelinated.
- Fast pain, stabbing and pricking.
C fibres - unmyelinated
- Slow pain, burning, throbbing, ache.
- Polymodal (different forms of sensory information involving more than 1 sense).
