endocrine, neurons, nervous system

Question 1

3 functions of myelin sheath

Answer 1

Act as an electrical insulator, prevents interference from nearby neurons
Protects axon from damage
Increases the impulse speed

Question 2

2 types of myelinated nerve fibres

Answer 2

Myelinated fibres (wt long axons)
unmyelinated fibres (short axons)

Question 3

Membrane potential

Answer 3

potential difference between inside and outside of cell.
Resting membrane potential is -70mV

Question 4

ion channels

Answer 4

Leakage channels
Voltage-gated channels
Sodium Potassium pump
ligand-gated ion channels (mechanical gated)
Mechanical-gated

Question 5

4 important properties of reflexes

Answer 5

A stimulus is required to trigger a reflex
A reflex is involuntary
A reflex is rapid
A reflex is stereotyped (same way each time)

Question 6

Central nervous system

Answer 6

consists of the brain and spinal cord

Question 7

Peripheral nervous system (PNS)

Answer 7

made up of: the nerves that carry info into the CNS - afferent (sensory), carry info away from CNS - efferent (motor), and ganglia - groups of nerve cell bodies outside of the brain and spinal cord.

Question 8

3 structures protecting (CNS)

Answer 8

1. bone - cranium encases the brain and the vertebral canal/column surrounds spinal column. Bones provide strong, rigid structure for protection.
2. Membranes called meninges
3. Cerebrospinal fluid

Question 9

meninges

Answer 9

3 layers of connective tissue forming membranes

Question 10

3 layers of meninges

Answer 10

Dura mater, outer most layer. Tough and fibrous, rubber like, sticks closely to cranium but not so in vertebral canal.
Arachoid mater, middle meningeal layer. Loose mesh of fibres
Pia mater, inner part. Delicate, contains many blood vessels and sticks closely to surface of the brain and spinal cord.

Question 11

Cerebrospinal fluid

Answer 11

Clear, watery fluid in sub arachnoid space around brain and canal in centre of spinal cord.
contains: water, salts, WBCs, glucose, amino acids, urea
Fills space between the middle and inner meningeal layers and circulate through cavities in the brain
CSF formed by blood in ventricles of the brain and is absorbed
After it circulates, it re-enters/returns to blood capillaries. 30ml every hour (about 100ml)
3 main functions: protection, support, transport.

Question 12

Structure of brain

Answer 12

Corpus Callosum
Cerebellum
Medulla oblongata
Hypothalamus
Cerebrum

Question 13

Convolutions

Answer 13

ridges produced by the folding of cerebral cortex
sulci, shallow downfolds
Fissures, deep downfolds

Question 14

5 stages of action potential

Answer 14

Stimulus
Depolarisation
Repolarisation
Hyperpolarisation (refractory period)
Return to resting potential

Question 15

Depolarisation

Answer 15

A nerve impulse occurs when a strong stimulus is applied to a neuron
threshold must be reached (15mV)
When neuron stimulated by a neurotransmitter, some Na+ channels open, the membrane becomes more permeable to Na+ ions and lets them into cell.
This inward Na+ movement changes the inside from -ve to +ve -> this is because there are more +ve Na ions than -ve ions.
If stimulus strong enough (-55mV), then voltage-gated Na+ channels open
this occurs until all Na+ voltage channels are open. (+30mV, membrane voltage)

Question 16

Repolarisation

Answer 16

Na+ channels close, at the same time, voltage-gated K+ channels open, this restores the -ve intracellular and +ve extracellular environment, decreasing membrane potential.
This restores the -ve intracellular and +ve extracellular environment
It decreases membrane potential
this restoration of change is known as repolarisation
As the wave of positive passes through - the membrane restores itself by actively pumping Na+ out of the cell.

Question 17

Hyperpolarisation

Answer 17

After the action potential, V-G K+ channels are slow to close, so too many K+ ions diffuse out of the neuron.
This makes the cell more negative than -70mV

Question 18

Refractory period

Answer 18

Once Na+ channels open, they quickly become inactivated, they are unresponsive to another stimulus.
they are unresponsive to another stimulus
Another action potential cannot be initiated during this time.
The membranes returns to rest by the Na+/K+ pump.

Question 19

Dendrites

Answer 19

Usually short and highly branched-that grow from the cell body. Increase surface area
receive nerve messages ie. information collectors.
Receive inputs from neighbouring neurons
They carry impulses toward the cell body
if enough inputs the cell’s Axon may generate a nerve impulse (output or input)

Question 20

Axon

Answer 20

Single, long, nerve fibres branches off the cell body.
it carries nerve impulses away from the cell body and pass it on to other nerve cells
One axon per cell (neutron)
at end: terminal branches (tube-like), axon terminals branches at end that connect to dendrites of other cells.

Question 21

Myelin sheath

Answer 21

White fatty material/casing/coating on axon produced by Schwann cells in the peripheral nervous system (PNS)
Is not continuous
they are separated by tiny gaps, called nodes, jumping from one to the next (100m/sec)
Outermost coil of Schwann cell is neurilemma - helps in the repair/regeneration of injured/ damaged nerves.
in CNS, brain and sc: myelin sheath produced by oligodendrocytes
White matter - myelinated fibres
grey matter - unmyelinated fibres

Question 22

Myelinated fibres (wt long axons)

Answer 22

most axons have a myelin sheath covering.
White matter of CNS - in parts of brain and in spinal cord and peripheral nerves.
Energy cost
take up more space.

Question 23

Unmyelinated fibres (wt short axons)

Answer 23

Axons do not have a myelin sheath
nerve message travels more slowly (1-10m/sec)
Seen in brain on outside as grey matter
are a ‘bundle’ of axons that are wrapped very thinly

Question 24

Neurons

Answer 24

regarded as electrically excitable cells because their cell membranes exhibit voltage changes in response to stimulation.
A very weak electric charge is produced: 10-100mV
Nerve impulses travel quickly, so body can respond rapidly to any change/danger

Question 25

nerve impulse

Answer 25

Electrochemical change that travels along the membrane of a nerve cell
the message carried by a nerve
It involves electric voltage brought about by the change in chemicals = due to the ion concentrations inside and outside of nerve cell.

Question 26

leakage channels

Answer 26

Open at all times
Na+ in, K+ out - down concentration gradient via facilitated diffusion
Limited number of Na+ Lchannels
large number of K+ Lchannels

Question 27

Voltage-gated channels

Answer 27

Only open when nerve is stimulated
voltage-gated Na+ channels close when the membrane potential -70mV voltage-gated K+ closed.

Question 28

Na+/K+ pump

Answer 28

Carrier (shape change when ions pass)
3 Na+ out
2K+ in
Against concentration gradient - ATP needed
active transport pump
This pump maintains/ regulates ion flow from 1 side of cell membrane to another
If stops, cells swell and burst

Question 29

Ligand-gated ion channels (mechanical gated)

Answer 29

Conducted ion flow in response to the binding of a neurotransmitter - to neuron.
respond to pressure stimulus

Question 30

Resting membrane potential and polarisation

Answer 30

resting membrane potential is the difference in charge between the outside (+) and inside (-) of the cell (weak electrical charge)
It is maintained by distribution of Na+ and K+ - 3Na+ actively pumped out, 2K+ actively pumped in (Na+/K+ pump)
when a membrane is maintained like this it is polarised and also at its resting membrane potential (-70 milliVolts)

Question 31

Cells of the nervous system

Answer 31

called neurons
They are highly specialised for receiving stimuli (from receptors) and transmitting information/messages in the form of electrical impulses
Basic organisation: dendrites - input, cell body, axons - output

Question 31

Cell body

Answer 31

soma
Roundish structure
composed of cytoplasm that contains the nucleus which contains DNA.
Is the control centre of the cell.
contains organelles: mitochondria, ribosomes, rough ER (nissl Bodies) and Golgi apparatus.
Cell body-directs metabolism.
NO role in producing nerve impulse (neural signalling)

Question 31

Reaction threshold for action potential

Answer 31

if stimulus causes a change strong enough of 15mV it can not be stopped therefore it is known as an all-or-none response
Threshold is -55mV

Question 31

main functions of cerebrospinal fluid (CSF)

Answer 31

1. Protection - acts as shock absorber during times of impact, cushioning the CNS from blows or shocks it may receive.
2. Support - the brain floats in fluid
3. Transport - provides nutrients and O2 to the brain and sc. cells and removes wastes - CO2 and toxic substances

Question 32

Meningitis

Answer 32

infection of the meninges caused by micro-organisms: virus, bacteria, amoebic meningitis
Bacteria M: vaccine available for newborn.
CSF fluid collected for diagnosis.

Question 33

Cerebrum

Answer 33

largest part of the brain (80%)
Consists of: outer cerebral cortex (grey matter 2-4mm thick/ cell bodies + dendrites + unmyelinated axons) below is: Basal Ganglia (grey matter, group of cell bodies)
cortex is folded in patterns to increase its surface area (convulsions)
Between these folds are grooves, either shallow sulci (sulcus) or deep downfolds called fissures.
the deepest is the longitudinal fissure.

Question 34

Left vs right cerebrum

Answer 34

each 1/2 joined to one 1/2 of your body by nerves (tracts) that go down.
Left 1/2 controls right side of body, right 1/2 controls left side of body.
2 hemispheres joined at the base of the longitudinal fissure by the corpus callosum - bundles of transverse nerve fibres (myelinated) which allow communication between the two hemispheres.
Deep inside brain (a 5th lobe) insula.

Question 35

Types of nerves in PNS

Answer 35

1. Cranial nerves: 12 pairs - arise from the brain, eg. Optic nerve, auditory, facial nerve. Most are mixed nerves = sensory + motor fibres, but not all
2. Spinal nerves: 31 pairs - arise from the spinal cord, eg. Cervical nerves, thoracic nerves. All are mixed nerves = sensory + motor fibres. Each nerve is joined to the spinal cord by 2 roots: (bundles and nerve fibres), vental root (front), dorsal root (back)

Question 36

Dorsal root (posterior)

Answer 36

contains axons of sensory neurons (afferent fibres).
Cell bodies in swellings called dorsal root ganglion

Question 37

ventral root (anterior)

Answer 37

Contains axons of motor neurons (efferent fibres)
cell bodies found in grey matter of spinal cord

Question 38

PNS divisions

Answer 38

1. Afferent division - keeps CNS aware of the external and internal environments
2. Efferent division - carry nerve impulses from CNS to effectors

Question 39

Afferent division (sensory division)

Answer 39

somatic sensory neurons are sensory nerve cells from receptors in the skin and around the skeletal muscles and joints (limbs)
Visceral sensory neurons - are those that take impulses from the internal organs into the CNS.

Question 40

efferent division (motor division)

Answer 40

Can be somatic - carry nerve impulses to the skeletal muscles, regulated by signals that arise in cerebrum.
autonomic division (involuntary) - carry messages to heart and glands, smooth muscle

Question 41

Automatic division

Answer 41

sympathetic division - produce responses that prepare the body for action. Enables the body to respond to stress, throws body out of the homeostatic balance. Stimuli needed. The neurotransmitter is noradrenaline
Parasympathetic division - maintain body during normal activity (homeostasis). Vagus nerve affects HR. Neurotransmitter is Acetylchloline. Self governing, controlling, involuntary activities.
the sympathetic and parasympathetic division work together but with opposing actions/effects.
Most organs/effectors have dual innervation, receiving nerve fibres from both branches of ANS - symp + parasymp.
opposing actions: excitatory/inhibitory and stimulation/relaxation.

Question 42

Motor pathway diff between somatic and ANS

Answer 42

somatic pathway (motor/efferent) - CNS to effector = 1 neuron. Nerve cell body in grey matter of spinal cord -> myelinated motor fibre -> Acetylchloline (ACH) (neurotransmitter) -> effector
Autonomic pathway (motor/efferent) - CNS to effector = 2 neurons needed to get to target organ. Nerve cell body in grey matter of spinal cord -> ganglion 1st synapses -> Neurotransmitter: ACH -> effector (noradrenaline)

Question 43

Fight or flight response

Answer 43

stimulus: process in brain -> message down nervous system -> muscles respond to threat.
Greater supply of O2 and glucose needed by muscles.
need an increase in blood flow to certain areas, structures.
Then, in threatening situations: SNS becomes dominant and allows body to flight or fly.