Neurons, Synapses, Hormones, Homeostasis

Question 1

Neurons

Answer 1

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

Question 2

Myelinated Nerve Fibres

Answer 2

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)

Question 3

What is Saltatory Conduction?

Answer 3

Impulses jumping between gaps in the myelinated fibres

Question 4

What is located in the gaps of the Myelinated nerve fibre?

Answer 4

Nodes of Ranvier

Question 5

Describe a resting potential

Answer 5

Due to an imbalance of + and - charges. membranes pump Na and K across the membrane to generate this potential. -ve inside + outside (-70mv).

Question 6

What are the 3 mechanics in creating resting potential?

Answer 6

1. Na K pump - 3Na out fro 2K in, creating a [] gradient.
2. Membrane is 50x more permeable to K than Na - K leaks back faster, creating a greater Na gradient than K.
3. charged proteins inside nerve also increase charged imbalances.

Question 7

Describe Action Potentials

Answer 7

Rapid change in membrane potential as an impulse travels along it. 2 parts:
1. Depolarization (- to +)
2. Repolarization (+ to -)

Question 8

Depolarization

Answer 8

Na channels open, Na diffuses into neuron along gradient. Reverses charge imbalances, inside is now + (+30mv)

Question 9

Repolarization

Answer 9

Na channels close, K channels open, K diffuses out down gradient. Inside is now -, channels stay open until –70mv

Question 10

Nerve Impulses

Answer 10

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.

Question 11

What is the refractory period?

Answer 11

prevents action potential moving backwards, Na and K pumps reset restoring resting potentials.

Question 12

Local Currents

Answer 12

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.

Question 13

Synapses

Answer 13

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.

Question 14

What are the 2 ways impulses are moved across synapses?

Answer 14

1. Electrically - action potential jumps to next cell, rare but can happen
2. Chemically - action potential triggers release of n-transmitters from synaptic terminals, triggering the action potential in the next cell

Question 15

What are the steps of synaptic transmission?

Answer 15

1. Nerve impulses reaches terminal end of pre-synaptic neuron
2. Depolarization causes Ca to diffuse into the neuron
3. Ca causes synaptic vesicles to move to the membrane and fuse together
4. N-transmitter in vesicles are released into the synaptic cleft by exocytosis
5. N-transmitters diffuse across cleft and bind to post-synaptic receptors
6. Binding of n-transmitters causes Na channels to open
7. Na diffuses into post-synaptic neuron, reaching threshold potential
8. Action potential is triggered

Question 16

Acetylcholine (ACh)

Answer 16

N-transmitters used in cholinergic synapses and between muscle fibres. Produced in pre-synaptic neurons (choline + acetyl). Stored in vesicles, released during synaptic transmission.

Question 17

What does ACh do?

Answer 17

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.

Question 18

Threshold Potentials

Answer 18

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.

Question 19

Homeostasis

Answer 19

Ability of an organism to maintain a stable internal environment. Maintained through a feedback loop of the endocrine system.

Question 20

Feedback loops

Answer 20

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.

Question 21

Hormones

Answer 21

• Chemical messages sent from one body part to another
• Communication and coordinates whole body
• Regulation of large scale changes (metabolism, growth)

Question 22

Glands

Answer 22

• Exocrine glands secrete other things (sweat, oil) into ducts
• Endocrine glands secrete hormones directly into blood

Question 23

Endocrine System

Answer 23

• Hormones in blood are directed to target tissues
• Action of the hormone changes condition of tissue
• Monitored through feedback, usually negative

Question 24

Regulation of Blood Glucose

Answer 24

• 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.

Question 25

Islets of Langerhans

Answer 25

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

Question 26

What happens when blood glucose is high?

Answer 26

Insulin from B cells decreases glucose by:
- Stimulates liver to convert glucose to glycogen
- Decreasing rate of glucose breakdown by respiration

Question 27

Diabetes

Answer 27

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).

Question 28

Difference between Type 1 and 2

Answer 28

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.

Question 29

Thyroxin

Answer 29

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.

Question 30

How does thyroxin affect the metabolsim?

Answer 30

• Raises basal metabolic rate
• Increases rate of protein synthesis
• Triggers growth

Question 31

Thyroxin and temperature regulation

Answer 31

• 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.

Question 32

Thyroxin deficiency

Answer 32

• 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

Question 33

Leptin and appetite control

Answer 33

• 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

Question 34

Discovery of leptin

Answer 34

• 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

Question 35

Leptin resistance

Answer 35

• Most obese people produce leptin but don’t respond to it
• Hypothalamus fails to respond

Question 36

Melatonin

Answer 36

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

Question 37

Circadian Rhythm

Answer 37

• 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