Neurons, Synapses, Hormones, Homeostasis Flashcards
Neurons
Have a cell body and a nucleus. Have dendrites, short branched nerve fibres that receive impulses. Have axons which are elongated nerve fibres that transmit nerve impulses sway from the cell. 3 types:
1. sensory
2. relay
3. motor
Myelinated Nerve Fibres
Axons are covered in a myelinated sheet, deposited by Schwann Cells. Made up of up to 20+ phospholipid bilayers. Allows impulses to travel quickly (200m/s)
What is Saltatory Conduction?
Impulses jumping between gaps in the myelinated fibres
What is located in the gaps of the Myelinated nerve fibre?
Nodes of Ranvier
Describe a resting potential
Due to an imbalance of + and - charges. membranes pump Na and K across the membrane to generate this potential. -ve inside + outside (-70mv).
What are the 3 mechanics in creating resting potential?
- Na K pump - 3Na out fro 2K in, creating a [] gradient.
- Membrane is 50x more permeable to K than Na - K leaks back faster, creating a greater Na gradient than K.
- charged proteins inside nerve also increase charged imbalances.
Describe Action Potentials
Rapid change in membrane potential as an impulse travels along it. 2 parts:
1. Depolarization (- to +)
2. Repolarization (+ to -)
Depolarization
Na channels open, Na diffuses into neuron along gradient. Reverses charge imbalances, inside is now + (+30mv)
Repolarization
Na channels close, K channels open, K diffuses out down gradient. Inside is now -, channels stay open until –70mv
Nerve Impulses
An action potential starting at the end of a neuron along the axon to the other end. Occurs b/c of the movement of ions that depolarize one section of the neuron triggering the depolarization of the adjacent section. Threshold potential of -50-55 mv, always moves in the same direction.
What is the refractory period?
prevents action potential moving backwards, Na and K pumps reset restoring resting potentials.
Local Currents
How the action potential wave progresses along the axon. Moves via local currents of ions that diffuse along the axon. A wave of depolarization and then repolarization along the axon.
Synapses
Junctions between cells in the nervous system. Impulses travel from sensory receptors via nerve cells to effectors. Neurotransmitters move the synaptic cleft to effect an impulse, more than 30n-transmitters.
What are the 2 ways impulses are moved across synapses?
- Electrically - action potential jumps to next cell, rare but can happen
- Chemically - action potential triggers release of n-transmitters from synaptic terminals, triggering the action potential in the next cell
What are the steps of synaptic transmission?
- Nerve impulses reaches terminal end of pre-synaptic neuron
- Depolarization causes Ca to diffuse into the neuron
- Ca causes synaptic vesicles to move to the membrane and fuse together
- N-transmitter in vesicles are released into the synaptic cleft by exocytosis
- N-transmitters diffuse across cleft and bind to post-synaptic receptors
- Binding of n-transmitters causes Na channels to open
- Na diffuses into post-synaptic neuron, reaching threshold potential
- Action potential is triggered
Acetylcholine (ACh)
N-transmitters used in cholinergic synapses and between muscle fibres. Produced in pre-synaptic neurons (choline + acetyl). Stored in vesicles, released during synaptic transmission.
What does ACh do?
Binds to receptor on post-synaptic membrane to initiate an action potential. Broken down by acetylcholinesterase, resultant choline is reabsorbed back into pre-synaptic neuron for reuse.
Threshold Potentials
Action potential only triggered if threshold is reached. Once potential is reached, depolarization.
Diffusion of Na raises potential, more channels open, positive feedback. If potential is not reached, Na is pushed back out and returns to resting potential.
Homeostasis
Ability of an organism to maintain a stable internal environment. Maintained through a feedback loop of the endocrine system.
Feedback loops
Negative: reverse of the change detected, effector works to reduces the change, thermoregulation.
Positive: Reinforces the change, effector works to induce the same effect, childbirth.
Hormones
- Chemical messages sent from one body part to another
- Communication and coordinates whole body
- Regulation of large scale changes (metabolism, growth)
Glands
- Exocrine glands secrete other things (sweat, oil) into ducts
- Endocrine glands secrete hormones directly into blood
Endocrine System
- Hormones in blood are directed to target tissues
- Action of the hormone changes condition of tissue
- Monitored through feedback, usually negative
Regulation of Blood Glucose
- Must be regulated because if too low respiration stops, if too high hypertonicity damages cells
- Insulin and Glucagon regulate [] through negative feedback loop.
- Insulin lowers glucose, and glucagon raises.
Islets of Langerhans
3 Cell Types:
1. Beta Cells - synthesize and secrete insulin, 60% of an islet
2. Alpha Cells - source of glucagon , 30% of islet
3. Delta Cells - produces somatostatin, less abundant
What happens when blood glucose is high?
Insulin from B cells decreases glucose by:
- Stimulates liver to convert glucose to glycogen
- Decreasing rate of glucose breakdown by respiration
Diabetes
Metabolic disease that causes high blood glucose levels. The body either doesn’t make enough insulin (1), does make insulin but doesn’t use it effectively (2).
Difference between Type 1 and 2
Type 1: Early onset, doesn’t produce insulin, autoimmune disease B cells destroyed.
Type 2: Late onset, insulin receptors desensitized by over exposure, controlled by lifestyle and diet.
Thyroxin
Secreted by thyroid gland to regulate the metabolic rate and body temp, contains 4 I atoms, targets all cells and is vital for growth and cell differentiation.
How does thyroxin affect the metabolsim?
- Raises basal metabolic rate
- Increases rate of protein synthesis
- Triggers growth
Thyroxin and temperature regulation
- Chemoreceptors in the hypothalamus sense body temp decreasing, causes release of thyroxine which triggers an increased metabolism in all body cells, increases generation of heat.
Thyroxin deficiency
- Metabolism is slower
- Caused by iodine deficiency, results in underproduction of thyroxine
- Can lead to a goiter, traps iodine allowing it to produce adequate thyroxine
Leptin and appetite control
- Appetite is controlled by the hypothalamus, when it receives hormone signals.
- Triggered by: Insulin from pancreas, PYY3-36 from small intestine, leptin from adipose tissue.
- Leptin has an N-C-C backbone
Discovery of leptin
- Discovered in 1994 by Friedman
- Made through transcription and translation
- All cells have the leptin gene, only expressed in fat cells though
- “OB” code, “ob” is recessive and won’t code
Leptin resistance
- Most obese people produce leptin but don’t respond to it
- Hypothalamus fails to respond
Melatonin
Produced by the pineal gland in the darkness, targets the pituitary and other glands. Effects:
1. High [] cause drowsiness and promote sleep
2. High [] drop core body temp
3. High [] reduce kidney production of urine
Circadian Rhythm
- 24hr cycle of most living things, continues even in light or darkness
- Jet lag results from an imbalance in the rhythm from travel
- Melatonin can reduce jet lag and promote sleep
