Part 1 Flashcards
Nerve bundle
Myelin sheath is made of Schwann cells wrapped around the axon
Myelin: insulating material
Demyelination = myelin is destroyed
e.g. multiple sclerosis
Types of Neurons
Sensory Neurons: transmit electrical impulses from sensory receptors to the CNS
Relay Neurons (Interneurons): move impulses within the CNS
Motor Neurons: take impulses from CNS to effectors (glands/muscles)
How the impulse is transmitted
Impulse begins when a neuron is stimulated by another neuron or by the environment
Electrical impulse moves in one direction:
Dendrites → Cell Body → Axon
Synapse: gap between two neurons
Neurotransmitters transfer the signal to the following neuron
No myelin = ~5-25 m/s
With myelin = ~10-120 m/s
How the impulse is transmitted
Neuron not transmitting an impulse: membrane has an electrical potential (voltage) called resting potential
Caused by the imbalance of K + and Na + across the membrane (Na + /K + antiport pumps) = polarization
Electric difference (voltage): -70mV
When there is a stimulus…
Na+ gates open = Na + enter the cell
Electrical potential of the cell changes
depolarization (normal charge is reversed) = +30mV
Action potential is recorded Na + channels close K + channels open repolarization occurs (charges back to normal)
K + channels stay open longer
hyperpolarization = -85mV (refractory period = prevents one impulse to catch up with another)
Stimulus = self-propagating
The Synapse
Synapse = gap between neurons
Action potential cannot cross gap: neurotransmitters carry the impulse
Neurotransmitters: stored in vesicles at the end of axons (glutamate, GABA, acetylcholine, norepinephrine, dopamine, serotonin, nitric oxide, etc)
Voltage gated ion (Ca+2) channels open → calcium flows inside neuron.
Calcium ions help vesicles fuse with presynaptic membrane → neurotransmitters are released into synaptic cleft
These bind with neuroreceptors on post synaptic membrane.
Voltage gated channels are activated = depolarization of axonal membrane.
Impulse is passed on to post-synaptic neuron.
Neurotransmitters = released and reabsorbed (re-uptake) by pre-synaptic neuron.
Synaptic Transmission
- Nerve impulse reaches terminal end of pre-synaptic neuron.
- Depolarization causes voltage-gated calcium channels to open. Ca^2+ rushes in.
- Ca^2+ causes synaptic vesicles to move to membrane and fuse.
- Neurotransmitters that were stored in the synaptic vesicle now diffuse across the synaptic gap.
- NTs bind with post-synaptic receptors. NTs are specific to the receptor.
- Sodium channels open, causing Na+ to enter, leading to depolarization of the post-synaptic neuron. An action potential is initiated. The nerve impulse is then propagated along the post-synaptic neuron.
- Enzymes in the synaptic gap then break down the NT. The products of this break down are taken up by the pre-synaptic neuron by active transport (hence the large number of mitochondria)
Endocrine System
Endocrine glands produce hormones that travel in the circulatory system.
Target tissue responds
Response affects the gland = NEGATIVE FEEDBACK
Body maintains stable internal conditions = HOMEOSTASIS
Blood pH, Temperature, Water balance, Glucose concentration, CO2 concentration, etc.
The Endocrine System
A stimulus is received and processed.
Hormones are secreted directly into the blood.
They are carried to the target tissues (the place of intended action).
The action of the hormone changes the condition of the tissue.
This change in monitored through feedback.
Most hormonal change results in negative feedback.
Key endocrine glands: Pineal gland Pituitary gland Thyroid gland Thymus Adrenal gland Pancreas Ovary (female) Testes (male)
Hormones
Insulin- Converts glucose to glycogen
glucagon- converts glycogen glucose
adrenaline- “fight or flight” increases heart rate
testosterone- sperm production, male body development
FSH- stimulates oocyte development
LH- develops endometrium
Oestrogen- stimulates ovulation (release of the egg)
progesterone- maintains endometrium
HCG- maintains high level of oestrogen and progesterone in pregnancy
Oxytocin- causes contraction of the uterus during childbirth
Homeostasis
Maintaining the internal environment of the body within safe limits.
Water balance- osmoregulation- around 90% of blood volume dehydration with water loss kidneys and hormones- excretion.
CO2 concentration- 10-13 kPa. Kidneys- excretion- ciculation- breathing and heart rate
Body temperature- thermoregulation- 36c- 38c Vasodilation and sweating or vasoconstriction and shivering
Blood glucose concentration 80mg- 110mg- pancreas and liver insulin and glucagon
Blood pH 7.35- 7.45- buffering agents kidneys- excretion- circulation- breathing and heart rate
Control of Body Temperature
Hypothalamus controls body temperature, preventing cooling/overheating
Skin arterioles: vasoconstriction (prevents heat loss) ; vasodilation (more blood near surface – heat is transferred out)
Shivering
Hairs with erector muscle
Sweat glands
Thermoregulation
Human core body temperature needs to remain at around 37c
Hypothermia occurs when the body’s core temperature drops too low for metabolic reactions to occur. Death below 32c.
Hyperthermia-heart stroke- occurs when the body’s core temperature gets too high and tissues are damaged. Above 40c is deadly.
A lot of heat is generated in the liver and carries around the body in the blood. Heat is lost through the skin- the larger the SA: Vol ration, the faster the rate of heat loss.
The hypothalamus and pituitary like the nervous and endocrine systems
Cold temperature changes are detected by cells in the skin and relayed through the hypothalamus. The hypothalamus relays the signal to the pituitary, which acts to release thyroid stimulating hormone (TSH). TSH is carried in the blood and acts upon the thyroid, causing the release of thyroid hormone. This is carries through the blood, acting on almost all cells, leading to increased heat production through metabolism.
stimulus- cold sensory neurons- cold receptor cells relay- hypothalamus effector- pituitary hormone 1- TSH gland-pituitary trarget cells: thyroid gland effect: release thyroid hormone traget cells: all cells effect: increase metabolism, get warmer
Control of Blood Glucose
Pancreas is an endocrine gland
It releases insulin ( cells) and glucagon ( cells)
Receptors present on liver cells
Negative feedback occurs
