Module 5 Flashcards
What part of a neurone transmits away from its cell body?
The axon
What are the main (structural) differences between motor and sensory neurones?
Motor neurones have no dendron, only dendrites, and sensory neurones have their cell bodies in the ‘middle’ of the cell, with axons and dendrons and roughly equal length
What does a Schwann cell do?
It lays down up to twenty phospholipid bilayers around some neurones, forming a ‘myelin sheath’
What are the gaps called between the sheaves of myelinated neurones?
Nodes of Ranvier
What do sensory receptors do?
Act as a transducer - they each convert one specific type of stimulus into a nerve impulse
Name the four broad types of sensory receptor?
Mechanoreceptor
Chemoreceptor
Thermoreceptor
Photoreceptor
Describe and explain the role of the Pacinian Corpuscle and how it works
The Pacinian Corpuscle is a mechanoreceptor abundant in the skin, fingers and feet, which detects pressure. When pressure is applied to the receptor, it stretches the stretch-mediated sodium ion channels in the membrane, causing sodium ions to flood into the dendron and fire an action potential
What is the approximate potential difference across a resting potential, and how is it maintained?
About -70mV. The sodium-potassium ion pump pumps 3 sodium out for every 2 potassium it pumps in. Almost all of the voltage-gated sodium ion channels are closed but most potassium ion channels are open - making an overall charge gradient across the axon. The neurone is ‘polarised’
Describe the events of an action potential
Stimulus triggers voltage-gated sodium ion channels to open - causing sodium ions to flood in. If the ‘threshold’ is exceeded, this influx causes other ion channels to open and more ions to flood in (positive feedback loop, at about +40mV the membrane, is considered depolarised
How is the membrane of a neurone repolarised?
The membrane becomes more permeable to potassium ions and hence, they diffuse out of the membrane down their electrochemical gradient, reducing the charge in the axon until ‘hyperpolarisation’ occurs (axon < -70mV) causing the potassium channels to close and allows the resting potential to be restored
How does the mechanism of action potential propagation ensure a unidirectional impulse?
The action potential propagates a ‘wave of depolarisation’ through the neurone, followed by its repolarization (known as the refractory period) stopping the impulse being conducted backwards. Think of it like a Mexican wave!
What is saltatory conduction?
When depolarization occurs only across the nodes of Ranvier, creating ‘local circuits’ to more efficiently transmit the impulse (It effectively ‘jumps’ the myelin sections)
Which 3 factors have the highest influence on an axon’s speed?
Presence of myelin sheath, Diameter and temperature
What is the strength of an impulse related to?
It’s frequency of impulse, NOT it’s speed or anything
What is the neurotransmitter released from cholinergic synapses, and what is the basic nature of the neurotransmitter?
AcetylCholine (ACh), excitatory (depolarises the membrane)
Name an Inhibitory neurotransmitter
GABA, inhibitory (hyperpolarizes the membrane)
What happens when an action potential reaches a typical synapse?
The action potential’s ‘wave of depolarisation’ causes voltage-gated calcium ion channels on the presynaptic knob to open, allowing calcium ions to flood in. The influx of calcium ions causes the vesicles in the presynaptic knob to fuse to the presynaptic membrane and release the neurotransmitter (say, ACh) by exocytosis, to diffuse over the synaptic cleft
What happens at the post-synaptic membrane when a neurotransmitter has been released?
The neurotransmitter (probably ACh) will attach to sodium ion channels on the postsynaptic membrane and cause them to open, thus allowing sodium ions to flood in and propagate the action potential
What happens to ACh after it has propagated the action potential?
It is hydrolysed by Acetylcholinesterase, which returns acetate and choline to the presynaptic knob to be regenerated
What are the two forms of neuronal summation?
Spatial and temporal
Describe briefly the main organisation of the mammaliam nervous system
CNS and PNS. From PNS leads Autonomic (subconscious) and Somatic. From Autonomic leads Sympathetic Motor (flight or flight) and Parasympathetic Motor (relax/slowing)
What are the features of somatic neurones?
Heavily myelinated
ACh transmitter
What are the features of autonomic sympathetic neurones?
Lightly myelinated preganglionic neurones
Unmyelinated postganglionic neurones
NA transmitter
What are the features of autonomic parasympathetic neurones?
Lightly myelinated preganglionic neurones
Unmyelinated postganglionic neurones
ACh transmitter
What does the cerebellum control?
Muscle movement and posture
What does the medulla oblongata control?
Contains regulatory centres and coordinates reflexes
What does the hypothalamus do?
Autonomic control hub, regulating sleep, hunger, aggression, blood composition, and temperature and also produces some hormones
What does the pituitary gland do?
Anterior: controls hormones like FSH etc.
Posterior: releases ADH
Describe the features of skeletal muscle
Voluntary, striated and regularly arranged. They contract quickly for short periods of time and are multinucleate
Describe the features of cardiac muscle
Involuntary, specially striated and branched (for simultaneous contraction) of an intermediate speed. Muscle is uninucleate and myogenic
Describe the features of smooth muscle
Involuntary, non-striated with no regular arrangement. Contract slowly, but for long periods of time. Also uninucleate
Describe the gross structure of muscle tissue
Bunches of myofibrils surrounded by a sarcoplasmic reticulum (containing the nuclei), encased by a sarcolemma, infoldings in the sarcolemma are called t-tubules
Describe the structure of myofibrils
A ‘lattice’ of Actin (thinner filament) and Myosin (thicker filament)
What is a sarcomere?
Functional unit of the muscle, one sarcomere is defined as the distance between two Z-bands
What is the sliding filament model/theory?
Myosin filaments pull Actin inwards towards the centre of the sarcomere. The sarcomere is shortened and the H-zone becomes narrower
When a muscle contracts, what happens to the length of the dark and light bands?
The light band gets narrower but the dark band remains the same length
Describe the mechanism of muscular contraction
When an impulse reaches an NMJ, the depolarization travels deep into the sarcolemma (down t-tubules) and opens calcium ion channels in the sarcoplasmic reticulum. The calcium ions bind to troponin pulling tropomyosin out of the way of the actin-myosin binding site. Once attached, the myosin head flexes and pulls the filament along, and releasing ADP. This lets ATP bind to the head of the myosin and pulls it off. The myosin head can re-attach further up and repeat. Think of it like the oars of rowing!
What is aerobic respiration used for?
Long periods of low-intensity exercise using ATP from oxidative phosphorylation
What is anaerobic respiration used for?
Short periods of high-intensity exercise using ATP from glycolysis, producing lactic acid from pyruvate
What are creatine phosphate reserves used for?
Instants of vigorously intense exercise using creatine phosphate to immediately reform ATP
What does the endocrine system do?
Secrete (hormones) from glands
What are the properties of steroid hormones?
Lipid Soluble
Bind to steroid receptors inside cells
Can facilitate or inhibit transcription