Lecture 2 A02 Nervous System 2025 V2

Action Potential

A large and rapid change in membrane potential (Em) in the positive direction followed by a return to resting potential.

Resting Membrane Potential

The electrical potential of a cell membrane when there is no stimulus.

Depolarisation

Membrane potential (Em) increases (becomes more positive).

Repolarisation

Membrane potential (Em) decreases (becomes more negative).

Hyperpolarisation

Em becomes more negative than the resting Em.

Threshold Potential

Em at which an action potential is generated.

Saltatory Conduction

The process by which action potentials 'jump' from node to node along myelinated axons.

Absolute Refractory Period

The phase during which no stimulus can generate a second action potential.

Synaptic Transmission

The process of communication between neurons, involving the release of neurotransmitters.

Neurons

The primary signaling cells in the nervous system, responsible for transmitting nerve signals.

Glial Cells

Support cells in the nervous system that maintain homeostasis, form myelin, and provide support and protection for neurons.

Myelin Sheath

An insulating layer around axons, formed by Schwann cells in the PNS and oligodendrocytes in the CNS.

Dendrites

Extensions of neurons that receive signals from other neurons.

Axon Hillock

The junction between the axon and the cell body where action potentials are initiated.

Synapse

The junction between two neurons where neurotransmission occurs.

Neurotransmitter

Chemical messengers released at synapses that transmit signals between neurons.

Presynaptic Cell

The neuron that releases neurotransmitters into the synaptic cleft.

Postsynaptic Cell

The neuron that receives the neurotransmitters and responds to them.

Na+/K+ ATPase

An enzyme that pumps sodium out and potassium into the cell, helping to maintain resting membrane potential.

Cation and Anion

Ions with a positive charge (cation) and ions with a negative charge (anion), essential in generating electrical signals in neurons.

Pineal gland

Melatonin

Hypothalamus

inhibits and releases ADH and oxytocin

pituitary

posterior pituitary: stores and releases ADH and oxytocin

anterior pituitary: numerous hormones

thyroid gland

thyroid hormones (T3 and T4)

parathyroid gland

parathyroid hormone

adrenal gland

adrenal medulla: catecholamines

adrenal cortex: steroid hormones

pancrease

insulin and glucagon

ovary

estrogen and progestin

testis

androgens

explain circulation hormones

• hormones synthesized in secretory endocrine system

• travels through blood

• binds with target cell

explain neurohormones

same thing as circulation hormones just secreted from neurosecretory neuron

explain paracrine and autocrine

paracrine: hormones bind to other cells

autocrine: hormones bind to itself

and both only travel within extracellular fluid and not the blood

explain amines

• stress hormone

• tyrosine based (hyrophilic)

• primarily secreted from adrenal medulla

• catecholamines

  • epinephrine (adrenaline)

  • norepinephrine (noradrenaline)

explain peptides

• interacts with cell receptors

• angiotensin

  • liver produces angiotensin which reacts with the kidneys production of renin

  • react together to create angiotensin 1

  • lungs have ACE that convert angiotensin 1 to angiotensin 2

  • angiotensin 2 effects blood pressure, water balance, and ion regulation

explain steroids

• derived from cholesterol

• lipophilic (hydrophilic)

• bind to receptors in cell and requires carrier proteins for blood transport

explain cell surface receptors (amine/peptide hormones)

• hormone secreted into blood

• hormone binds to receptor

• signal transduction

  • signal receptor takes hormone into signal transduction pathway

  • ATP converts into ADP

• cellular response

  • cytoplasmic (open ion channel)

  • nuclear (alter transcription)

explain intracellular receptors

• hormones secreted from cell and travels into blood stream

• hormones pass the plasma membrane

• hormone binds to receptor

  • nucleus

  • cytosol

• receptors interact to gene to alter transcription

explain The Hypothalamus and the Posterior Pituitary

• hypothalamus produces oxytocin and ADH

• hormones travel down axon

• hormones are released into blood stream

  • oxytocin stimulates uterine contraction and milk production

  • ADH causes water retention by kidneys (less urine production)

diuresis

increases urine flow

anti-diuresis

prevents increase in urine flow

what other two hormones does the hypothalamus produce

• releasing hormones (RH)

  • stimulate the release of hormones synthesized in the endocrine cells

• inhibiting hormones (IH)

  • inhibits the release of hormones synthesized in the endocrine cells

what do beta cells do

release insulin and lowers blood glucose

what do alpha cells do

release glucagon and raises blood glucose

where does the Thyroid-StimulatingHormone(TSH) come from and what does it do

• thyroid gland

• increases rate of metabolism

where does the Adrenocorticotropic Hormone (ACTH) come from and what does it do?

• adrenal gland (cortex)

• stress response and renergy regulation

Neuromuscular junction

• motor nerve (motor neuron) meets a muscle (muscle fibre)

• nerve releases a chemical called acetylcholine (Ach) which binds to receptors on the muscle triggering an electrical signal (AP) causing the muscle to contract

• calcium must enter the nerve terminal in order for exocytosis to occur

what is the synaptic cleft

the space between the presynaptic and postsynaptic cells

what are fascicle

muscle fibres surrounded by connective tissues

muscles are made of bundles known as …

fascicles

what do each fascicle contain

• muscle cells (fibres)

  • long

  • multi nucleated cells

  • myofibrils

  • responsible for contractions

what are muscle fibres surrounded by

a membrane known as the sarcolemma

what is inside the muscle fibres

• myofibril

  • repeating units of sarcomere

    • sarcomeres contain thin actin and thick myosin filaments for contraction

describe the actin (thin filament)

• consists of 2 strands of actin molecules (double helical strand)

  • each one has a binding site for myosin

• tropomyosin

  • long regulatory protein (at rest) blocks the myosin (thick filament) binding sites on actin molecules

troponin?

• regulatory protein complex that binds

  • actin (thin filaments)

  • tropomyosin

  • Ca++

describe the myosin (thick filament)

• consists of 2 intertwined subunits (with a head and tail)

  • subunit heads have

    • actin binding sites

    • ATPase site

      • ATP → ADP + Pi (organic phosphate)

• thick filaments are made up of hundreds of myosin molecules

myosin energy states

• myosin heads can have a high or low energy state

• myosin in a low energy states have the heads pointing inwards (to the centre of the sarcomer)

• myosin in a high energy state has the heads pointing outwards (towards the end of the sarcomer)

why is the binding of myosin and actin important and what does it form

• important for muscle contractions

• forms a crossbridge

regulation in muscle contraction

• acetycholine (neurotransmitter) released from neuro junction and produces ATP to travel down T-tubules

• signals calcium release and binds to troponin forming crossbridge

• crossbridge separates and calcium returns to SR

force generation

• myosin and actin are separated using ATP (low energy state)

• ATP hydrolosizes and becomes ADP and Pi separating the myosin and actin

• Pi flies away

• myosin starts to slowly head towards the low energy state and ADP flies away

isometric contraction

tension increases muscle doesnt shrink (plant)

isotonic contraction

tension increases and muscle shrinks (pushup)

which species have closed circulatory systems

all vertebrates

explain blood flow in the human (mammalian) heart

• vena cavea

• right atria

• valve

• right ventricle

• semilunar valve

• pulmonary arteries

• lungs (capillaries)

• pulmonary veins

• left atria

• valve

• left ventricle

• semilunar valve

• aorta

• systemic circuit (capillaries)

describe the cephalopods circulatory system

• afferent

• branchial hearts (2)

• gills

• efferent

• systemic heart

• cephalic aorta

• gills

• major veins

what 4 chambers does a fish have

1 sinus venosus

1 atria

1 ventricle

1 bulbus arteriosus

summarize what non crocodilian reptiles have

2 atria

2 ventricle

left aorta

right aorta

pulmonary artery

summarize what amphibians have

2 atria

1 ventrical

1 conus arteriosus

summarize what mammals have

2 atria

2 ventrical

aorta

pulmonary artery

how does circulation in water (gill) breathing fish occur

• heart

• ventral aorta

• gills

• dorsal aorta

• systemic circulation

• hearts

circulation in lungfish

• left ventricle

• gills

• dorsal aorta

• systemic circulation

• right atria

• right ventricle

• gills

• pulmonary artery

• lungs

• left atria

amphibian circulation (deoxygenated blood)

• tissues

• sinus venosus

• right atria

• ventricle

• conus arteriosus

• pulmocutaneous arteries

• lungs/skin

amphibian circulation (oxygenated blood)

• lungs

• pulmonary vein

• left atria

• ventricle

• conus arteriosus

• systemic arteries

• systemic circulation

crocodile hearts (what do they have)

2 atria

2 ventricles

left aorta

right aorta

pulmonary artery