Nervous System + Muscles

Question 1

What is the central nervous system (CNS)?

Answer 1

The brain and the spinal cord

Question 2

What is the peripheral nervous system (PNS)?

Answer 2

All of the nerves in the body

Question 3

What are the three types of nerves in the somatic nervous system?

Answer 3

• Sensory nerves: carry impulses from receptors on sense organs to CNS
• Motor neurons: carry impulses from CNS to effectors (muscles/glands)
• Spinal nerves: found in spinal cord and are a mixture of sensory and motor neurones

Question 4

What is a receptor?

Answer 4

Transducers which convert energy from another form into electrical impulse

Question 5

What do sensory neurones do?

Answer 5

Carry impulses from receptors to the CNS

Question 6

What is the role of relay (intermediate) neurones?

Answer 6

Connect sensory and motor neurones within the CNS- found entirely within the CNS

Question 7

What is the function of motor neurones?

Answer 7

Carry impulses from the CNS to effectors (muscles or glands) they have a large cell body and highly branched dendrites to provide SA for axon terminals of other neurons and are almost entirely in the CNS

Question 8

What is the myelin sheath and why is it important for neurons?

Answer 8

Some neurones are myelinated, their axon is insulated by a myelin sheath with small uninsulated sections along its length (called nodes of Ranvier)
The myelin sheath is formed by specialised cells known as Schwann cells which wrap themselves around the axon.
This means that electrical impulses do not travel down the whole axon, but jump from one node to the next so only leakage of ions in unmyelinated regions which reduces resistance to impulse meaning it gains electrical potential energy at every node (saltatory conduction)

Question 9

What is saltatory conduction?

Answer 9

The jumping of electrical impulses from one node of Ranvier to the next

Question 10

What is the resting potential of a neuron?

Answer 10

-70mV

Question 11

What do sodium-potassium pumps do in maintaining resting membrane potential of neurons?

Answer 11

Sodium-potassium pumps are present in the membranes of neurones
Actively transport 3 sodium ions out of the axon for every 2 potassium ions that they actively transport in
Larger concentration of positive ions outside the axon than there are inside the axon
The movement of ions via the sodium-potassium pumps establishes an electrochemical gradient

Question 12

What is the role of protein channels in neurones?

Answer 12

The cell-surface membrane of neurones has selective protein channels that allow sodium and potassium ions to move across the membrane by facilitated diffusion
The protein channels are less permeable to sodium ions than potassium ions
This means that potassium ions can diffuse back down their concentration gradient, out of the axon, at a faster rate than sodium ions- leaky channels

Question 13

What triggers an action potential?

Answer 13

Caused by brief change in charge distribution across a neuron membrane
Stimulus: triggers sodium ion channels in the membrane to open allowing sodium ions to diffuse into the neurone down an electrochemical gradient. Stimulus can either be an electrical impulse from another neurone or a chemical change to the membrane of the neurone. If stimulus large enough threshold potential is reaches and can become an actional potential

Question 14

What happens during depolarisation in an action potential?

Answer 14

threshold potential (-55mV) reached s voltage gated sodium channels open causing Na+ to diffuse into axon reducing P.D across enzyme membrane which triggers more sodium ion channels to open causing more depolarisation in positive feedback mechanism. AP reached around +30mV

Question 15

What occurs during repolarisation in an action potential?

Answer 15

1ms after AP reached all voltage gated Na+ ion channels close and K+ voltage gated ion channels open causing diffusion of K+ ions out of axon returning to resting potential in negative feedback

Question 16

What is hyperpolarisation during an action potential? How does the neuron return to resting potential?

Answer 16

Hyperpolarisation: K+ ion channels slow to close so too many K+ ions diffuse out causing P.D to become more negative
Return to resting potential: K+ ion channels close and Na-K pump returns cell to resting potential so Na+ sensitive to depolarisation again

Question 17

What is the all-or-nothing principle?

Answer 17

very weak or below a certain threshold, the receptor cells won’t be sufficiently depolarised and the sensory neurone will not be activated to send impulses
If the stimulus is strong enough to increase the receptor potential above the threshold potential then the receptor will stimulate the sensory neurone to send impulses
This is an example of the all-or-nothing principle
An impulse is only transmitted if the initial stimulus is sufficient to increase the membrane potential above a threshold potential
Rather than staying constant, threshold levels in receptors often increase with continued stimulation, so that a greater stimulus is required before impulses are sent along sensory neurones

Question 18

What is the refractory period?

Answer 18

Period where both sodium (repolarisation) and potassium (hyperpolarisation) ion channels closed so axon membrane is unresponsive- max frequency of impulses = 1/time of refractory period

Question 19

What factors affect the speed of conduction in neurones?

Answer 19

Myelination: travel faster when myelinated by saltatory conduction
Diameter: thicker = faster as axon membranes have greater SA over which ions can move so faster rate of depolarisation, greater volume of cytoplasm so decreases electrical resistance

Question 20

What occurs during transmission across synapses?

Answer 20

electrical impulse arrives at the end of the axon on the presynaptic neurone (synaptic knob) neurotransmitters are released from vesicles at the presynaptic membrane
The neurotransmitters diffuse across the synaptic cleft and temporarily bind with receptor molecules on the postsynaptic membrane
Stimulates the postsynaptic neurone to generate an electrical impulse that then travels down the axon of the postsynaptic neurone
The neurotransmitters are then destroyed/ recycled to prevent continued stimulation of the second neurone, which could cause repeated impulses to be sent

Question 21

What is summation in the nervous system?

Answer 21

single impulse insufficient to generate AP so combination of stimuli can trigger response and avoids overwhelming nervous system with impulses. Temporal (impulses arrive in quick succession of each other causing combined effect) or spatial (multiple impulses arriving at separate synaptic knobs can stimulate same cell)

Question 22

Describe transmission across a cholinergic synapse?

Answer 22

Action potential at the presynaptic membrane causes depolarisation of the membrane
Stimulates voltage-gated calcium ion channel proteins to open
Calcium ions (Ca2+) diffuse down an electrochemical gradient from the tissue fluid surrounding the synapse into the synaptic knob
This stimulates ACh-containing vesicles to fuse with the presynaptic membrane, releasing ACh molecules into the synaptic cleft by exocytosis
The ACh molecules diffuse across the synaptic cleft and temporarily bind to cholinergic receptors in the postsynaptic membrane
Causes sodium ion channels to open- Na+ diffuse down electrochemical gradient into cytoplasm of postsynaptic neurone
The sodium ions cause depolarisation of the postsynaptic membrane, re-starting the electrical impulse once the threshold is reached
The ACh molecules are broken down and recycled
This prevents the sodium ion channels staying permanently open and stops permanent depolarisation of the postsynaptic membrane,
The enzyme acetylcholinesterase catalyses the hydrolysis of the ACh molecules into acetate and choline
The choline is absorbed back into the presynaptic membrane and reacts with acetyl coenzyme A to form ACh, which is then packaged into presynaptic vesicles ready to be used when another action potential arrives

Question 23

What happens when an action potential reaches the presynaptic membrane?

Answer 23

Depolarization causes voltage-gated calcium ion channels to open

Question 24

What role does acetylcholinesterase play at the synapse?

Answer 24

Catalyzes the hydrolysis of ACh to prevent continuous stimulation

Question 25

What is the function of dopamine? How is deficiency treated?

Answer 25

involved in muscle control eg in Parkinsons producing insufficient amount s agonist drugs (have same effect as dopamine by binding to receptors) or precursor drugs (used to synthesise dopamine)

Question 26

What effect does cocaine have on neurotransmission?

Answer 26

binds to dopamine transporter protein acting as competitive inhibitor so dopamine accumulates at synapses to stimulate feelings of pleasure

Question 27

What is the role of the hypothalamus in the brain?

Answer 27

connected to pituitary gland and releases hormones based on detections in blood or stimulates pituitary gland to secrete hormones. Thermoregulation, Osmoregulation, Regulates digestion (peristalsis, enzymes and hunger), Endocrine function control

Question 28

What is the structure and function of skeletal muscles?

Answer 28

Function: Responsible for moving the rigid skeleton of mammals.
Muscle Fibres:
Made up of muscle fibres surrounded by CM.
Muscle fibres are highly specialised, multinucleated cells.
The muscle fibres contain an organised arrangement of contractile proteins in the cytoplasm.
Parts of Muscle Fibres:
Cell surface membrane = sarcolemma.
Cytoplasm = sarcoplasm.
Endoplasmic reticulum = sarcoplasmic reticulum (SR).
The sarcolemma has deep tube-like projections called T-tubules that run close to the SR.
Sarcoplasm Components:
Contains mitochondria for aerobic respiration to generate ATP for muscle contraction.
Contains myofibrils, bundles of thin actin and thick myosin filaments creating bands, which slide past each other during muscle contraction.
Sarcoplasmic Reticulum (SR):
Contains protein pumps that transport calcium ions into the lumen of the SR

Question 29

What is the role of the cerebellum?

Answer 29

Controls involuntary motor coordination

Question 30

What is the function of the medulla oblongata?

Answer 30

cardiac (control of HR), vasomotor (control of muscle contraction in arterial walls to regulate BP), respiratory (controls BR) centres

Question 31

What are Pacinian corpuscles?

Answer 31

Each receptor only responds to a specific stimulus to differentiate between internal and external environment
Different types of receptors can detect pressure or temp on the skin and number can vary eg fingertips large amount
Pacinian corpuscles are a type of receptor found deep in the skin at ends of sensory neuron axons
They are present in the skin of fingers, soles of the feet as well as in joints, tendons and ligaments.
Made of layers of membrane separated by gel containing Na+ ions
The section of axon surrounded by layers of membrane contains stretch-mediated sodium ion channels which open when sufficient pressure is applied causing membrane layers to be distorted
When pressure receptors are stimulated by pressure on the skin an electrical potential difference across the axon membrane is established - the generator potential due to excess Na+ conc surrounding axon
Na+ ions enter axon via facilitated diffusion leading to depolarisation of the membrane which creates generator potential which triggers action potentials to carry impulse to CNS

Question 32

What is visual acuity?

Answer 32

The ability to distinguish between two separate points

Question 33

What are rods and cones in the retina?

Answer 33

Rods: sensitivity to light intensity- breakdown of rhodopsin (ONLY IN DIM LIGHT) optical pigment results in generator potential, allow humans to distinguish between light and dark objects and are sensitive to low light intensities DO NOT SEE COLOUR
Cones: sensitivity to wavelength of light/colour- breakdown of iodopsin (ONLY IN BRIGHT LIGHT) optical pigment results in generator potential, are less sensitive to light, sense different wavelengths of light (red sensitive, blue sensitive and green sensitive pigments- combined effect allows humans to see all colours)

Question 34

What is the fight-or-flight response?

Answer 34

Sensory neurones detect environmental stimuli associated with danger and send impulses to the brain
The amygdala (a small region of the brain located in the cerebrum) sends impulses to various other parts of the brain, including the hypothalamus
The hypothalamus is stimulated to send impulses via the sympathetic nerves to the adrenal glands
This causes the adrenal medulla to secrete the hormone adrenaline (dilates bronchioles to increase airflow to alveoli, stimulates contraction of iris muscles to dilate pupils, vasoconstriction of blood to skin and gut AND ALL OTHER EFFECTS)
At the same time, the hypothalamus also releases a peptide hormone that stimulates the anterior pituitary gland to release ACTH (adrenocorticotropic hormone)
ATCH is transported to the adrenal glands via the bloodstream
This causes the adrenal cortex to secrete the hormone cortisol
Cortisol stimulates target organs and tissues to increase blood pressure, blood glucose ensuring the tissues have sufficient glucose and oxygen needed for rapid response
Cortisol also suppresses the immune system

Question 35

Describe transmission across a neuromuscular junction

Answer 35

Neuromuscular Junctions: Located between a motor neurone and a muscle cell, similar to synapses.
Impulse Arrival: When an action potential reaches the presynaptic membrane of the motor neurone, calcium ions diffuse into the neurone.
Neurotransmitter Release: Calcium ions stimulate vesicles containing acetylcholine (ACh) to fuse with the presynaptic membrane, releasing ACh into the synaptic cleft.
Binding to Muscle: ACh binds to receptor proteins on the muscle cell’s sarcolemma, opening ion channels for sodium ions to enter.
Depolarisation: Sodium influx depolarises the sarcolemma, generating an action potential that travels down T-tubules towards centre of muscle fibre.
Calcium Release: The action potential triggers voltage gated calcium ion channels in the sarcoplasmic reticulum (SR) to open, releasing calcium ions into the sarcoplasm surrounding myofibrils.
Troponin Activation: Calcium binds to troponin, causing a shape change that moves tropomyosin on the thin actin filaments, exposing myosin-binding sites.
Muscle Contraction: This initiates the sliding filament model of muscle contraction.
Stopping Contraction:
Acetylcholinesterase breaks down ACh to stop stimulation in synaptic cleft.
Calcium ions are pumped back into the SR, ending muscle contraction after sarcolemma, T tubules and SR is not polarised.

Question 36

What is the role of ATP in muscle contraction?

Answer 36

ATP is required for:
Myosin to detach from actin.
Hydrolysis of ATP for myosin to return to its original shape.
Active transport of calcium ions back into the sarcoplasmic reticulum.
ATP sources:
Resting muscles have a small ATP store (lasting 3-4 seconds of intense activity).
Mitochondria produce ATP aerobically, but this is slow.
Anaerobic respiration begins quickly but takes time to generate ATP.

Question 37

Describe the structure anf function of smooth muscle

Answer 37

unconscious control of body parts, including walls of blood vessels and the gut by controlling blood flow and causing vasoconstriction.
Structure:
Contains both actin and myosin filaments, but does not have the striation or banding seen in skeletal muscle.
Cells are small, elongated, and spindle-shaped with one nucleus.

Question 38

What is the structure and function of cardiac muscle?

Answer 38

Present only in the heart.
Myogenic: Can contract without external stimulation from nerves or hormones.
Non-fatiguing: Does not tire and can contract continuously throughout an individual’s life.
The fibres form a network through the walls of the atria and ventricles.
Fibres are connected by intercalated discs.
Contains a large number of mitochondria to supply ATP for continual contraction.

Question 39

What is antagonistic muscle action?

Answer 39

Muscles work in pairs, with one muscle contracting while the other relaxes as they are only capable of contracting.
Example: In the arm, the bicep contracts to raise the lower arm while the tricep relaxes, and vice versa to lower the arm.

Question 40

What role do tendons play in muscle function?

Answer 40

Connective Tissue: Tendons, which are lengths of strong, flexible connective tissue, attach muscles to bones.
Tendons do not stretch during muscle contraction.
Some muscles have long tendons or are directly attached to the bone.

Question 41

What occurs at the neuromuscular junction?

Answer 41

An action potential triggers calcium ions to diffuse into the motor neurone, leading to neurotransmitter release

This process initiates the muscle contraction cycle.

Question 42

What is the structure of filaments in a myofibril?

Answer 42

Thick filaments are made of myosin molecules, which are fibrous proteins with a globular head.
The fibrous part anchors the myosin molecules in the thick filament, with their globular heads pointing away from the M line.
Thin filaments are made of actin molecules (globular proteins) that form chains. Two actin chains twist together to form a thin filament.
Tropomyosin, a fibrous protein, wraps around the actin chains, and troponin is attached to the actin chains at regular intervals.

Question 43

Describe the muscle contraction process in the sliding filament model

Answer 43

Contraction: Sarcomeres within myofibrils shorten as actin and myosin filaments slide past each other
Myosin heads bind to actin, forming cross-bridges.
Myosin heads bend (power stroke), pulling actin toward the sarcomere center.
ADP is released when myosin bends.
ATP binds to myosin, allowing detachment from actin.
ATP is hydrolyzed by myosin ATPase to return the head to its original position.
The myosin head binds to a new actin site and repeats the cycle.
Process continues until the muscle is fully contracted, provided ATP is available and troponin/tropomyosin are not blocking myosin-binding sites.

Question 44

How is muscle contraction stopped?

Answer 44

Acetylcholinesterase breaks down ACh to stop stimulation in synaptic cleft.
Calcium ions are pumped back into the SR, ending muscle contraction after sarcolemma, T tubules and SR is not polarised.

Question 45

What is the purpose of phosphocreatinine in muscles?

Answer 45

provides rapid ATP and creatine production by transferring a phosphate to ADP.
Phosphocreatine is used during short bursts of intense activity until mitochondria can supply ATP.
After phosphocreatine is used up, the rate of muscle contraction depends on aerobic and anaerobic ATP production.

Question 46

What are fast muscle fibres?

Answer 46

Contract rapidly and rely on anaerobic respiration (need large amounts of calcium ions due to rapid contraction and relaxation cycle and fasting binding of myosin heads.
Fatigue quickly due to lactate production.
High proportion in human eye cells
Fewer capillaries (slow supply of oxygen and glucose), low myoglobin, which makes them paler.

Question 47

What are slow muscle fibres?

Answer 47

Contract more slowly and rely on aerobic respiration.
Fatigue less quickly, suited for endurance.
High proportions in human back muscles to keep skeleton erect
Have more capillaries (short diffusion distance and high proportion of respiratory substrates), myoglobin + haemoglobin, and mitochondria, making them dark red.

Question 48

What is the effect of training on muscles?

Answer 48

People generally have a mix of fast and slow fibres in their arm and leg muscles.
Effects:
Short-burst, high-intensity training increases fast fibres (e.g., sprinters, weightlifters).
Endurance training increases slow fibres (e.g., marathon runners, cyclists).
Training can also increase capillaries and mitochondria in muscles + type of muscle fibre.

Question 49

How is action potential transmitted across an axon?

Answer 49

The current causes the opening of sodium ion channels a little further up the axon
This causes an influx of sodium ions in this section of the axon generating an action potential in this direction
The previous section of the axon is in the repolarisation stage (the sodium channels are closed and potassium channels are open) and is unresponsive
This makes the action potentials discrete events and means the impulse can only travel in one direction

Question 50

What is the importance of the refractory period?

Answer 50

ensures that action potentials are discrete events,
It ensures that ‘new’ action potentials are generated ahead (ie. further along the axon), rather than behind the original action potential, as the region behind is ‘recovering’ from the action potential that has just occurred- impulse only travels in one direction
The existence of the refractory period also means that there is a minimum time between action potentials occurring at any one place along a neurone

Question 51

What is the difference between excitatory and inhibitory neurotransmission?

Answer 51

Excitatory: stimulate generation of AP (open gated sodium ion channels) in postsynaptic membrane and inhibitory (open gated potassium ion channels + can develop overtime) does opposite to prevent random impulses so if they both arrive together it cancels out

Question 52

What is the effect of cannabis’s on the nervous system?

Answer 52

binds to presynaptic receptors at neuromuscular junctions to close Ca2+ ion channels leading to decreased muscle contraction eg could help in MS (causes damage to myelin sheath)

Question 53

What is the effect of MDMA on the nervous system?

Answer 53

stimulates release of serotonin which can cause euphoria, enhanced touch and body sensation

Question 54

What is the function of the cerebrum?

Answer 54

vision, hearing, memory, thinking, speech- 5 lobes with cerebral hemispheres (right controls left side of body and vice versa) joined by corpus callosum (nerve fibres), white matter contains myelinated axons of neurones

Question 55

What is the function of the cerebral cortex?

Answer 55

thinner outer layer of cerebrum consisting of grey matter- cell bodies of neurones with highly folded membrane to increase SA for nerves

Question 56

What is the function of the pituitary gland?

Answer 56

anterior pituitary (produces and secretes hormones) + posterior pituitary (stores and secretes hormones produced by hypothalamus)

Question 57

Describe a reflex arc

Answer 57

Doesnt involve conscious part of the brain to prevent delay due to synapses- quicker (blinking, control of light in eye, pain stimulus, saliva production, swallowing)
stimulus is detected by a receptor
The sensory neurone sends electrical impulses to the spinal cord (the coordinator)
Electrical impulses are passed on to relay neurone in the spinal cord
The relay neurone connects to the motor neurone and passes the impulses on
The motor neurone carries the impulses to the effector generating a muscle contraction or response

Question 58

What process affects visual acuity?

Answer 58

Synapses connecting rod and cone cells to bipolar neurons which connect to ganglion neurons via synapses that have axons that extend to the optic nerve which can stimulate the brain to form a pattern for an image.

Question 59

Describe the visual acuity in rod cells

Answer 59

Lower in Rod cells: multiple rod cells synapse with single bipolar neuron cell and multiple bipolar neuron cells synapse with a single ganglion cell so brain unable to interpret which impulse connects to each rod cell so only general idea of whether it is light or dark

Question 60

Describe the visual acuity in cone cells

Answer 60

Higher in cone cells: each cone cell corresponds with a bipolar neuron cells and the same for ganglion cells so brain can stimulate each spot of light to each cone cell

Question 61

Describe the effects of summation of rod and cone cells on visual acuity?

Answer 61

Summation: single stimulated rod is unlikely to produce generator potential large enough to stimulate bipolar cell for nerve conduction. Combined generator potentials are required to reach threshold. Allows humans to see in much dimmer light

Question 62

What is the structure and function of different parts of the eye?

Answer 62

Question 63

What are the 2 different types of responses from the autonomic nervous system?

Answer 63

Can be parasympathetic (rest or digest) or sympathetic (fight or flight eg. release of adrenaline)

Question 64

How does the medulla oblongata control heart rate?

Answer 64

Medulla: cardioregulatory centre of the brain:
Acceleratory: when activated impulses sent alng sympathetic neurones to SAN, noradrenaline secreted at synapse with SAN causing increase in frequency of electrical waves leading to increased HR
Inhibitory: when activated sent along parasympathetic neurones so acetylcholine secreted at synapse with SAN reducing frequency of electrical waves which causes resting heart rate

Question 65

What are stimuli which activate the medulla?

Answer 65

1. Change in internal conditions due to exercise: CO2 levels rise in blood, fall in blood pressure due to vasodilation of muscle arterioles
2. Detected by pressure receptors and chemoreceptors in aorta and carotid artery
3. Low frequency impulses from receptors = activates inhibitory centre to slow heart rate/ High frequency impulses from receptors = activates acceleratory centres to increase heart rate

Question 66

What is present in different bands of muscles?

Answer 66

Question 67

How is posture and complex body movement controlled by muscles?

Answer 67

Posture Maintenance: Muscles maintain posture by both contracting in an antagonistic manner to keep joints at a fixed angle (isometric contraction).
Complex Movements:
Lifting heavy objects involves coordination of multiple muscles for hand gripping, wrist rotation, and shoulder stabilisation, controlled by the brain.

Question 68

Why are muscles and bones needed for movement?

Answer 68

Muscles require an incompressible skeleton (bone) to produce effective movement, as muscles can only pull and cannot push.
Muscle Contraction: Muscles contract to produce movement, but they require a bone to pull on, as bone does not bend or shorten.