Biology-nerves, and nervous system (pre DP)

Nervous systems neuron structure Hormones Homestatis The human Brain

Medulla oblongata

Controls automatic and homeostatic activities:

swallowing and vomiting, digestion, breathing and heart activity

Cerebellum

coordinates uncuncious functions:

balance and movements, hand-eye coordination

Hypothalamus

• maintains homestasis using bothe the nervous and endocrine systems

• produces the hormones that are secreted by the posterior pituitary gland

• sends releasing factors to stimulate hormone secretion by the anterior pituitary gland

Pituitary gland

• posterior lobe stores and secretes hormones produce by the hypothalamus

• anterior lobe produces and secretes hormones that regulate many body functions

Cerebral hemispheres

• recives impulses for the eye, ear, nose and tongue

• acts as the integrating centre ffor higher copmplex functions: learning, memory, emotions and cosciousness

Hormones

chemical messengers which are made in one part of the body (in glad cells), and transported in the blood to work at another part of the body

hormones made

in gland cells

hormones transported

in the blood

Insulin

• produced by beta islet cells in the pancreas.

• lowers blood glucose levels

• works on the liver and large muscles

Glucagon

• produced by alpha islet cells in the pancreas

• increases blood glucose levels

• works on the liver and large muscles

ADH (Anti-diuretic hormone)

• produced by the pituitary gland in the brain

• conserves water by making ruine more concentrated

• works in the kidney

Adrenaline

• produced in the adrenal glands

• increases heart rate

• works on the heart

HGH (Human Growth Hormone)

• produced by the pituitary gland in the brain

• regulates bone and muscle growth

• works on all cells

Thyroxine

• produce by the thymus

• regulates metabolism (only reason you need iodine)

• works on all cells

Melatonin

• produced by the pineal gland

• hormone that makes us sleepy

• affected by light/dark level

Leptin

• hormone secreted onto the blood from adipose tissue

• formed in the adipose tissue

• regulates the energy balance by supressing hunger

Homostasis

• keeping the internal body conditions within a narrow range, even if external conditions change

• uses the nervous system and/or the endocrine system

• examples: body temprature, blood glucose levels, pH, CO2 level in the blood, water salt balance

negative feedback

• regulation. Where a receptor checks cnditions, and if the conditions are wrong, turns on “something” to correct the condition, then when it is back at normal level, turns that “something” off. (like a car temp.regulating)

Body temprature

• regulated by the hypothalamus of the brain

• if temprature is too cold: shivering (produces extra heat from the generation of ATP fo rthe movement of the muscles)

• Hairs stand up (create a layer of insulation so heat stays nea the body)

• metobalism can increase (extra ATP production produces waste heat)

• no sweating

• if temprature is too warm: sweating, evaporation of water on your skin takes energy from the body, which cools the body

• lowering of metabolism. less heat production by cells

• hairs lay flat. Reduces insulation

• No shivering

• humans can handle range of 36-37.5 boyd temp.

Blood sugar level

• regulated by the pancreas

• blood glucose level rises—> after eating

• Pancreas detects the rise of the glucose level and the beta cells of the pancreas produce the hormone insulin, which is then released in the bloodstream

• after reaching the cells on the target organs (liver and large muscles), it binds to receptros on the cell membrane and causes glucose from the blood to be taken up by these cells—>lowering the blood glucose level

• glucose is cahnged into the polysachride glycogen for storage in these organs

• the pacreas detects the blood glucose level as within normal range, and truns off the production of insulin

Negative feedback in homeostasis (ex.)

• After fasting or a long night’s sleep, the blood level drops

• the pancreas monitors this and the alpha-islet cells of the pancreas produce the hormone glucagon, which enters the bloodstream

• at the target organs of the liver and the large muscles, glucagon binds to the cells and causes the glycogen to be changed into glucose and released into the blood stream, raising the blood glucose level

• when the level reaches normal limits, the production of glucogon is stopped

Normal range of blood glucose level in a healthy human

70 mg/dL (3.9 mmol/L) and 100 mg/dL (5.6 mmol/L)

Diabetes

• desease due to elevated blood glucose levels

• long term effects: kidney disease, circulation problems with the possibilty of more infections, slow healing and loss of limbs, or retinal problems—>blindness, nerve damage.

Diabetes type 1

• young (8-15 years old)

• Cellular cause: B-islet cells do not produce insulin

• Cause: Auto-immune disease, own immune system attacks its own B-islet cells

• treatement: insulin injections, small meals, lower sugar intake, monitoring blood glucose levels

Diabetes type 2

• age: old (over 40)

• cellular cause: receptor cell on target organs do not react to insulin

• Cause: too much sugar, overweight

• treatment: Diet and exerxise, less sugar

Somatic nervous system (SNS)

the system that we can control, like most skeletal muscular movements

Autonomic nervous system (ANS)

the system we can not control, like most of the smooth muscles in our digestive tract, the cardiac muscle in our heart, the muscles in our pupils which constricr dilate our pupil, our reathing rate

Breathing rate (two opposing systems)

sympathetic nervous system (SNS) prepeares the body for action

1. heart rate increases

2. breathing increases

3. bronchi dilate

4. pupils dilate

5. digestion slows, enzymes stop production

parasympathertic nervous system (PNS) returns body to rest conditions

1. heart rate decreases to normal

2. breathing rate decreases

3. digestive enzyme can be made

Central Nervous System (CNS)

includes

• brain

• spinal cord

• neurons in those parts

Periferal Nervous System (PNS)

includes

• nerves going to (sensory neurons) and from (motor neurons) the CNS.

Periferal Nervous System (PNS)

12 pairs of cranial nerves-emerge directly from the brain

• sensory nerves

• motor nerves

• mixed nerves

those nerves control the head, face, neck and shoulders except the vagus nerve, which controls the internal organs.

31 pairs of spinal nerves- emerge from segments of the spinal cord

• mixed nerves that take impulses to and from the spinal cord

Neuron Structure

A specialized cell of the nerous system to carry information

PARTS:

• dendrite

• cell body with nucleus

• axon

• axon terminal (motor end plate, synaptic knobs)

myelinated neuron

has a:

• myelin sheath around the axon

• made of insulating fatty Shwann cells

• Shwann cells: protect the neuron and support it

myelin sheath

made of:

• insulating fatty Shwann cells

Shwann cells

• protects the neuron and support it

• make impulse travel faster—> the impulse will hop between these cells (Nodes of Ranvier) instead of going the whole axon (Saltatory conduction)

Saltatory coduction

when an electrical node skips from node to node down the full length of an axon

direction of impulse

1. from the dendrites

2. through the cell body

3. to the axon

4. and then to the axon terminal

Neuron communication

Electrical:

• within one neuron

  • uses differences in ion concentrations (Na⁺ K⁺Cl⁻ mainly)

Chemical:

• between a neuron and another cell since the neuron does not touch the other cell

• neurotransmittors are used to send message across the synaptic cleft (gap) between the cells

Electrical communication

Resting potential (Rp)

• when a nerve is not firing and is negative (since there are more negative ions inside the neuron than the outside of it)

• Rp is -70 mV

• inside are K⁺ and large anions (neg charge).

• Outside is Na⁺ and Cl⁻

Action potentioal

• when an impulse in generated. Potential is positive, since the inside of the neuron becomed more positive than the outside, due to Na⁺ ions coming in. Action potential is around +35mV

Resting Potential

when a nerve is not firing and is negative. Since there are more negative ions inside the neuro than the outside of it.

Action potential

when an impulse is generated. potential is positive, since the inside of the neuron becomes more positive than the outside.

transmission of an impulse within a neuron

Resting potential

i

• is maintained by active transport of K⁺ and Na⁺ ions, using ATP energy and Protein pumps in the membrane of the neuron.

• 3 Na⁺s are pushed out of the neuron an 2 k⁺s are pulled into the neuron.

• The neuron is said to be in the polarized phase

ii.

• When the neuron is stimullated , Na⁺ Channels open and Na⁺ enters the neuron, raising its potential.

• If the potential is raised ove -50mV (the threshold potential) there will bea an Action potential, and mor Na⁺ xomes in, until the potential reaches about +35mV.

• The phase is called De-polarization

iii

• K⁺ channels open and let out k⁺ from the inside of the neuron, this causes the potential to decrease again, (repolarization phase)

iV

• more Na⁺ inside the neuron and K⁺ outside the neuron, and this needs to be changed, so the active transport of the Na/K pump works to restore resting potential and maintain it.

V

• Propagation of the impulse along the neuron

  Myelinated neurons: Saltatory, the impulse hops between the nodes of Ranvier
  

• Non-myelenated neurons: Where the Na⁺ entered, and before it is pumped out again, it diffuses down the neuron a little way, causing the next Na⁺ channel to open, and let in more Na⁺  at this area; his happens the whole way down to the axon terminal.

threshold potential

potential tha goes over -50mV

De-polarization

loss of the difference in charge between the inside and outside of the plasma membrane of a muscle or nerve cell due to a change in permeability and migration of sodium ions to the interior.

Repolarization phase

whn k⁺ channels open and let out k⁺ from the inside othe neuron, which causes the potential to decrease again.

1. Chemical communication between neurons and other cells

1. 1. The impulse reaches the axon terminal (Na⁺ has entered and there is an action potential in this region) of the pre-synaptic neuron.

   2. This causes Ca²⁺ channels open and Ca²⁺ enters the synaptic knobs in the axon terminal.

   3. This causes vesicles with a specific neurotransmitter to move towards the cell membrane at the end of the synaptic knob.

   4. The vesicles fuse with the membrane and release the neurotransmitter by exocytosis.

   5. The neurotransmitter diffuses across the synaptic cleft from high concentration by the pre-synaptic neuron to low concentration near the post-synaptic neuron. 

   6. The neurotransmitter binds to specific receptors (glycoproteins) on the post-synaptic cell’s membrane

   7. This causes Na⁺ channels to open on this cell, and let in the Na⁺, and an action potential is now generated in the post-synaptic cell. (if the neurotransmitter should inhibit an impulse, Cl^- could be let in instead, and cause hyperpolarization of the post-synaptic cell, which makes it harder to reach threshold potential)

   8. The neurotransmitter is then taken up again by the post synaptic cell to be re-used. Often, an enzyme is required to break it down into smaller molecules to be able to be taken into the cell. One example is the neurotransmitter acetylcholine. The enzyme is acetylcholinesterase. (Some drugs work by blocking this enzyme, causing less re-uptake, so that more neurotransmitttor stays in the synapse, and keeps affecting the post-synaptic cell.

   9. Active transport is also used to pump the ca²⁺ ions out of the pre-synaptic cell, which stops the vesicles from releasing their contents. 

medicines and drugs

1. A medicine can inhibit the enzyme in the synaptic cleft that breaks down the neurotransmitter so there is more around in the synapse.

2. A medicine can mimic the neurotransmitter and bind to the receptor on the post-synaptic membrane:

   1. This can work like the real neurotransmitter. Ex. Alcohol makes GABA (inhibitory neurotransmitter) work more – slows things

   2. This can block the real neurotransmitter from binding and working. Ex. Alcohol blocks glutamate from exciting cells – slows things

3. A medicine can bind to receptors on the re-uptake channels in the pre-synaptic neuron

   1. This can block re-uptake. Ex Cocaine stops re-uptake of dopamine leaving too much dopamine in the synapse

This can “confuse” the pre-synaptic neuron into doing something it should not.

Reflex

1. a rapid unconscious response to a stimulus (change in the environment)

   1. Controlled by the autonomic system

   2. Often useful for survival (obtaining food or avoiding danger)

   3. The brain is not involved, just a sensory neuron to the CNS and a motor neuron leaving the CNS (and sometimes an interneuron between these)

   4. Examples: blink reflex protects the eye, pupil reflex protects the retina from too much light, grip reflex in babies, dive reflex in babies is used in baby swim classes, knee jerk reflex, pain withdrawal reflex