Animal Responses: Candidates should be able to: (a) discuss why animals need to respond to their environment; (b) outline the organisation of the nervous system in terms of central and peripheral systems in humans; (c) outline the organisation and roles of the autonomic nervous system; (d) describe, with the aid of diagrams, the gross structure of the human brain, and outline the functions of the cerebrum, cerebellum, medulla oblongata and hypothalamus; (e) describe the role of the brain and nervous system in the co-ordination of muscular movement; (f) describe how co-ordinated movement requires the action of skeletal muscles about joints, with reference to the movement of the elbow joint; (g) explain, with the aid of diagrams and photographs, the sliding filament model of muscular contraction; (h) outline the role of ATP in muscular contraction, and how the supply of ATP is maintained in muscles; (i) compare and contrast the action of synapses and neuromuscular junctions; (j) outline the structural and functional differences between voluntary, involuntary and cardiac muscle; (k) state that responses to environmental stimuli in mammals are co-ordinated by nervous and endocrine systems; (l) explain how, in mammals, the ‘fight or flight’ response to environmental stimuli is co-ordinated by the nervous and endocrine systems.

The Brain

Cerebrum: Highly folded area at the front of the brain made of two hemispheres.

Corpus Callosum: Bridge of tissue that connects two hemispheres of the cerebrum.

Medulla Oblongata: Link between the brain and spinal chord. Coordinates and controls involuntary movements such as breathing, heart rate and movements of the wall of the alimentary canal (smooth muscle in gut wall)

Hypothalamus: regulates the autonomic nervous system and controls the secretion of hormones from the pituitary gland. It controls our homeostatic processes such as temperature regulation and water content of bodily fluids.

Cerebrum: Structure & Function

Primary visual area

Wernicke’s area: understanding language: association area

Sensory areaMotor area

Broca’s area: produces language: motor area

Auditory lobe

Auditory association area Visual

Association Area

Cerebrum: Structure & FunctionThe cerebrum is divided into two hemispheres which are connected via the corpus callosum. The outermost layer is folded and consists of a thin layer of nerve cell bodies known as the cerebral cortex. It is this area of the brain that is in control of higher order brain functions such as conscious thought and emotional response, the ability to override some reflexes and features associated with intelligence such as reasoning and judgement.

Cerebral

cortex

Sensory Areas

Association areas

Motor Areas

Receive impulses directly from receptors.Somatosensory area mapping shows it is subdivided according to areas of body from which it receives information.

Link between sensory and motor areas.Compares input with previous experience in order to interpret what the input means and judge an appropriate response.

Send impulses to effectors (muscles and glands) via motor neurones

The cerebral cortex is subdivided into areas responsible for specific activities:

The BrainFrontal Lobe controls conscious motor movement, speech, thought and personality.

Parietal Lobe interprets information from the sensory cortex about touch, pressure, pain and temperature.

Occipital Lobe receives sensory information from the eyes.

Temporal Lobe receives sensory input from ears – perception of language.

Cerebellum controls the coordination of movement and posture. The cerebellum receives impulses from the ears, eyes and stretch receptors in muscles and this information is integrated and used to coordinate the timing of skeletal muscle contraction and relaxation. When we go on ‘autopilot’, we are using our cerebellum: it contains programmed information. The cerebellum is responsible for keeping us upright, judging the position of objects and limbs, tensioning of muscles to manipulate tools and instruments and operation of antagonistic muscles to coordinate relaxing and contracting.

Organisation of the Nervous SystemLiving organisms are able to respond to changes in both external and internal environments. We need a method of communication between sensors and effectors. Animals need to coordinate lots of different responses, from coordinated voluntary muscle action to fine control of balance, posture and temperature regulation.

Central nervous System

Brain and Spinal Chord

Peripheral Nervous System

Somatic nervous system

All sensory neurones and

motor neurones to skeletal muscle

Autonomic nervous system

Sympathetic

Motor neurones that supply the internal organs

(viscera)

Parasympathetic

Motor neurones that supply the internal organs

(viscera)Receptors and sensory neurones

transmit impulses to the CNS

In the spinal chord, there is a region ion the centre that

contains unmyelinated neurones (grey matter)

and a regions around the outside that contains axons

and dendrons that are mainly myelinated and

therefore appears white.

Sensory neurones that carry impulses in from the receptors and motor neurones that that carry action potentials out to effectors.

All of the neurones that carry impulses into and out of the CNS:

Organisation of the Peripheral Nervous SystemThe peripheral nervous system is split into two systems: the somatic nervous system and the autonomic nervous system. The somatic nervous system includes all the sensory neurones and motor neurones that take information to skeletal muscle. All of the neurones in a typical reflex arc are part of the somatic nervous system. The autonomic nervous system is itself divided into 2 components: theses are the sympathetic and parasympathetic.

Autonomic nervous System: Sympathetic

The axons of the preganglionic neurones pass out of the spinal chord through the ventral route

The preganglionic neurones synapse with the motor neurones in an autonomic

ganglion

From these autonomic ganglia, motor neurone axons pass to all of the organs in the body.

The neurotransmitter that carries impulses across the

synapses in the sympathetic nervous

system is noradrenaline.

The sympathetic nervous system is activated when we encounter stimuli that make us scared or put us under stress . The sympathetic nervous system therefore helps to prepare the body for fight or flight.

Autonomic nervous System: Parasympathetic

All of the nerve pathways involved in the parasympathetic all begin in the brain, the top of the spinal chord or the very base of the spinal chord. The neurone that carries the impulse out of the brain or spinal chord carries on going until it is inside the wall of the organ that it will stimulate. The motor neurone will synapse with an effector neurone inside of the organ.

Many of the axons of the neurones of the parasympathetic system are in the vagus nerve.

The neurotransmitter at synapses in the parasympathetic system is acetylcholine. This often has an inhibitory effect on some organs. In general, the parasympathetic system helps the body to ‘rest and digest’.

Parasympathetic Sympathetic

Most active in sleep and relaxation Most active in times of stress

Neurones from CNS linked at a ganglion within the target tissue: pre-ganglionic neurones vary in length

Neurones from CNS linked at an autonomic ganglion just outside of the spinal chord: pre-ganglionic neurones are therefore very short.

Neurotransmitter is acetylcholine Neurotransmitter is noradrenaline

Autonomic nervous System: Comparing the Sympathetic and Parasympathetic

Effects of Sympathetic Stimulation: Increases rate and force of contraction of heart Dilates pupils Ciliary muscles relax so lens is thinner for distant vision Sphincter muscles contract Liver releases glucose into blood Increases sweating Pili erector muscles contract so hair stands on end Vasoconstriction of arterioles to gut and skin Ventilation rate and depth increases

Effects of Parasympathetic Stimulation: Reduces rate and force

of contraction of heart Pupil constricts Increase in glycogen

production

Neuromuscular JunctionSkeletal muscle contracts when it receives an impulse from a neurone. Neurones and muscles meet at specialised synapses called neuromuscular junctions.

1. Action potential arrives at neurone: calcium ion channels open and calcium ions diffuse into presynaptic neurone. This causes vesicles, containing neurotransmitter (generally acetylcholine) to move to and fuse with the presynaptic membrane. Neurotransmitter released into cleft by exocytosis.

2. Neurotransmitter binds to receptors on the sarcolemma. Sodium ions channels open and Na+ ions flood in. This causes a depolarisation across the membrane and initiates an action potential.

3. Depolarisation of sarcolemma spreads down the T tubules. Ca2+

channels open and Ca2+

ions diffuse out of the sarcoplasmic reticulum. The ions will bind to troponin molecules that are attached to actin filaments. This causes contraction.

Comparing synapses and neuromuscular junctions

Synapses Neuromuscular Junction

Neurone to Neurone Neurone to Sarcomere

Post synaptic stimulation leads to action potential in post synaptic neurone

Action potential leads to depolarisation of sarcolemma and muscle contraction

Synaptic knob is smooth and round

End plate is flattened up to muscle fibre with microvilli appearance

Neurotransmitter located in vesicles in presynaptic membrane

Vesicles release neurotransmitter into cleft on stimulation

Neurotransmitter diffuses across the cleft and binds to post synaptic membrane

Binding of neurotransmitter results in depolarisation of post synaptic membrane

Enzyme present to degrade neurotransmitter to avoid continual stimulation of post synaptic membrane.

Structure of Skeletal Muscle Skeletal muscle is described

as being striated. It appears to have stripes or bands of

light and dark.

Region Description

A band Darker regions of the sarcomere, where the thick protein filament myosin is present.

Darkest part of A band

Where myosin and actin filaments overlap

H band Lighter areas of the A band where only myosin is present

M line Provides attachment for myosin filaments

I band Lighter areas of the sarcomere where the thin actin filaments are

Z line Provides attachment for actin filaments

M line

When a muscle contracts...

H band gets shorter – there is less area in which there is only myosin present.

I band and A band stay the same: the actin and myosin filaments themselves don’t get shorter.

Darkest part of the A band (where the actin and myosin overlap) gets longer.

The distance between Z lines decreases when a muscle contracts – the sarcomere gets shorter.

The Sliding Filament ModelAs muscles contract, the sarcomeres in each myofibril get shorter as the Z lines are pulled closer together.

The Sliding Filament Model

When a muscle is relaxed,

the tropomyosin and troponin

are in such a

position in the actin

filament that

prevents

myosin from

binding.

When the

action potential stimulates the release of Ca2+

ions from the

sarcoplasmic

reticulum, the Ca2+

flood the muscle

cell. The Ca2+

bind to troponin: the

troponin

changes shape and the tropomyosin moves in order

to expose

the myosin binding site. The myosin is then able to bind to actin,

forming a cross bridge.

The myosin heads

tilt, causing the actin

to be pulled

along so overlap more

with the myosin

filament. ADP

and Pi are

released. This is

the power

stroke.

New ATP attaches

to the myosin head as

the cross

bridge is

broken. The ATP

is hydroly

sed, providing enough energy

to force the

myosin heads

to release

the actin.

They tip back to

their previous condition and are

then able to repeat

the process, forming a cross bridge further along the

filament.

The role of ATP in muscle contractionATP is required for muscle contraction: after the power stroke, ATP must be hydrolysed in

order to provide enough energy to break the cross bridge connection between actin and myosin and re-set the myosin head forwards. The myosin head can then attach to the next binding site along the actin molecule and bend again.

ATP is also necessary in the presynaptic neurone, prior to the neuro-muscular junction. Energy is required to release neurotransmitter into the cleft by exocytosis.

ATP

ATP supplies in muscles are used up very rapidly once the muscle starts working. There are 3 mechanisms by which ATP supply is maintained: 1. Aerobic respiration in muscle cell mitochondria (dependent on

supply of oxygen to the muscles and the availability of respiratory substrates)

2. Anaerobic respiration in the muscle cell sarcoplasm – this leads to the production of lactic acid, which is toxic. This stimulates increased blood supply to the muscles.

3. Creatine Phosphate: in the muscle sarcoplasm, there are stores of this molecule. A phosphate group can easily be removed from the Creatine phosphate and combined with ADP to produce more ATP by the enzyme creatine phosphotransferase.

When a person dies, respiration stops and ATP production ceases. Calcium ions can no longer be pumped into the cisternae of the sarcoplasmic reticulum, so they build up in the sarcoplasm. This causes troponin and tropomyosin to move away from their blocking positions on the actin filaments, so myosin heads are able to bind with the actin. There is no ATP left to provide energy to break the cross links, so the myosin heads remain firmly attached to the actin filament.

Rigor mortis lasts for up to 3 days. By the end of this time, enzymes leaking out of lysosomes will have partially destroyed the cells, and the actin-myosin bridges will have broken apart.

Rigor Mortis: the rigidity of deathIn resting muscle, most myosin heads are not attached to actin filaments. Transporter proteins pump calcium ions into the cisternae of the sarcoplasmic reticulum, so troponin and tropomyosin cover the attachment sites.

No ATP, so the cross links between the myosin and actin filaments cannot be broken, so muscles are held rigidly.

Voluntary Muscles Location?Attached to skeleton

Function?Movement of skeleton at joints

Structure? Striated Muscle cells form fibres

containing several nuclei Each fibre is surrounded by a

plasma membrane called a sarcolemma. The sarcoplasm of a muscle cell contains lots of mitochondria, extensive sarcoplasmic reticulum (specialised endoplasmic reticulum) and myofibrils comprised of actin and myosin myofilaments.

Stimulus?Somatic Nervous System

Contraction/fatigue?Contracts quickly and powerfully; fatigues quickly.

Involuntary (smooth) Muscle

Stimulus?Innervated by autonomic nervous system – not under voluntary control.

Contraction/fatigue?Relatively slow contraction; tires very slowly

Location Function

Walls of intestine Peristalsis – moving food along intestine

Iris of eye Control intensity of light entering eye: contraction of radial muscles dilates pupil; contraction of circular muscles constricts pupil.

Walls of arteries and around arterioles

Temperature regulation, regulation of local blood pressure and redirecting of blood to voluntary muscles during exercise.

Structure? Spindle shaped Bundles of actin and myosin Single nucleus Circular bundles in walls of arteries

and walls of cervix and uterus Circular and radial bundles on iris of

eye Circular and longitudinal bundles in

walls of intestine

Location?Muscular part of heart: atrial muscle, ventricular muscle and specialised excitatory and conductive muscle fibres (SAN, AVN)

Function?Coordinated contraction of heart to pump blood

Structure? Striated Intercalated discs fuse in such a way that

there are gap junctions with free diffusion of ions so action potentials can pass quickly and easily between cardiac muscle fibres.

Contraction/ fatigue?Never fatigues; powerful contraction

Cardiac Muscle Stimulus?Some cardiac muscle capable of stimulating contraction without nervous impulse – this is myogenic.Autonomic nervous system regulates rate of contraction. Sympathetic nerves increase rate; parasympathetic nerves decrease rate.

Muscles, Nerves and Hormones: The Fight or Flight Response

1. Cerebral understanding of threat activates hypothalamus

2. Hypothalamus stimulates increased activity of sympathetic nervous system

3. Sympathetic nervous system activates the adrenal medulla: adrenaline is released

4. Hypothalamus releases Corticotrophin Releasing Factor which stimulates…

5. Anterior Pituitary gland to release Adreno-corticotrophic hormone (ACTH)

6. ACTH arrives at adrenal cortex. This stimulates the release of approximately 30 corticosteroid hormones. The fight of flight response

makes an organism ready for the actions that lead to confrontation of the danger or escape from it.

A stressor is a stimulus that causes the stress response.