5.4.2

Andy Todd 1

thebiotutor.com

A2 Biology OCR

Unit F215: Control, genomes and environment

Module 4.2 Animal responses

Notes & Questions

5.4.2

Andy Todd 2

Discuss why animals need to respond to their environment.

Animals need to be able to coordinate a vast set of responses if they are to stay alive

These range from voluntary muscle actions to enable fight or flight to the fine control of balance, posture and temperature regulation

Outline the organisation of the nervous system in terms of central and peripheral systems in humans. &

Outline the organisation and roles of the autonomic nervous system.

The nervous system allows humans to be receptive to their internal and external environment, make sense of the stimuli and respond to these stumli in a way that improves their chances of survival

The nervous system comprises of a central and peripheral system that must work together to bring about these response to the stimuli

The Nervous System

Central Nervous System CNS

Sensory Neurones

Peripheral Nervous System PNS

Motor Neurones

Somatic System Autonomic System

Made up of Billions of neurones Grey matter – unmyelinated White matter - myelinated

Receptor CNS myelinated

CNS Effectors (muscles & glands)

CNS Skeletal muscle Conscious control Myelinated 1 neurone involved

CNS Smooth muscle Cardiac muscle Glands Unconscious control Non-myelinated 2 plus neurones involved Ganglion present

Sympathetic pathway Parasympathetic pathway

Stress Short pre-ganglionic neurone Ganglion close to Spinal cord Nor-adrenaline Increase heart rate Pupil Dilates

Relaxation Pre-ganglionic neurone vary Ganglion close to target tissue Acetylcholine Decrease heart rate Pupil constricts

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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.

Structures

Cerebrum

o Largest part of the brain

o Divide into two hemispheres

Cerebral Cortex

o Outer surface of the cerebrum

o Thin layer of nerve cells

o More highly developed in humans than any other organism

Cerebellum

o Over half the neurones in the brain

Corpus Callosum

o Holds the two cerebral hemispheres

Medulla Oblongata

o Found in the inner brain near the top of the spinal cord

Hypothalamus

o Found in the inner brain

Functions

Cerebrum

o Associated with being Human

o Higher brain function

Conscious thought

Emotional responses

Overriding of reflexes

Reasoning and Judgement

Cerebral Cortex

o Divided into regions

o Sensory areas

Receive impulses directly from sensory receptors

o Association areas

Compares inputs from previous experiences in order to interpret what the input means and judge an appropriate response

o Motor areas

Sends impulses to effectors (muscles and glands)

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corpus callosum

thalamus

hypothalamus

pituitary body

medulla oblongata cerebellum

pineal body

cerebrum

cerebralcortex

corporaquadrigemina

Front

Cerebellum

o Motor processing

Fine control of muscular movements

Body posture

Balance

Dexterity

Non-conscious operations E.g walking or driving a car etc

o Sensory processing

The retina neurones

Balance organs in the inner ear

Receptors from joints

Medulla Oblongata

o Controls breathing rate (respiratory centre)

o Controls smooth muscle

o Controls Heart rate (cardiac centre)

Hypothalamus

o Controls the autonomic nervous system

o Controls the endocrine glands

o Homeostatic mechanisms

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A

B

C

D

Cerebrum

Pituitary gland

Cerebellum

Medulla Oblongata

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Describe the role of the brain and nervous system in the coordination of muscular movement.

Functions of the Cerebellum

Maintaining muscle tone and posture

Coordination of voluntary motor activity

Maintenance of balance

Cerebellum and Muscle Tone

The cerebellum has neural connections with other parts of the brain and the peripheral parts of

the body. So at any given moment it continuously receives sensory information from the bones,

joints and muscles about their position, rate and direction of movement and forces acting on

them.

The cerebellum in turn conveys this information to the motor control centers of the cortex

(motor cortex) setting the background tone and posture so that the cortex can execute new

movements based on intent. In other words, the cerebellum tells the motor cortex in what

position a limb already is and what it is doing so the cortex can plan its next move.

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Cerebellum and Motor Control

The cerebellum also continuously receives information on the sequence of movements desired by

the motor control areas of the cortex. With regard to movement coordination, the cerebellum

behaves like a computer, constantly comparing the actual movement of the muscle groups with the

motions intended by the motor cortex.

In case of a difference between the two, the cerebellum immediately sends signals to the muscle

groups to correct the movement so that the desired effect can be achieved, much like computers

calculating and correcting the flight path of airplanes or space vehicles.

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Describe how coordinated movement requires the action of skeletal muscles about joints, with reference to the movement of the elbow joint.

The Elbow Joint

Muscle that control the elbow joint

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Operation of the neuromuscular junction

Explain, with the aid of diagrams and photographs, the sliding filament model of muscular contraction.

The skeletal muscle has contractile organelles called microfibrils

These microfibrils contract by sliding filaments over each other

Each microfibril is made up of many microfilaments of which there are two types

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Myosin filaments

o Myosin (or thick Myosin) filaments contain many myosin molecules

o Two globular heads

o One tail

Actin Filaments

o Consists of two actin filaments (F-actin) wrapped around each other

o Each actin filament is made of individual globular actin monmers (G-actin)

o The two actin filaments are held together by Tropomyosin – a rod shaped protein

o The thin actin filament also includes Troponin which has 3 polypeptides

One to bind to G-actin

One to bind to tropomyosin

One to bind calcium ions

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Arrangements of these filaments

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Relaxed Muscle Contracted Muscle

A Band (Myosin Filament) Same length Same Length

I Band (Band of no over lap - Actin Only) Longer Shorter

H Band (Band of no over lap - Myosin Only) Longer Shorter

Sarcomere (from Z-line to Z-line) Longer Shorter

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The Power stroke

An action potential reaches the dendrite at a neuromuscular junction

Acetylcholine is released by exocytosis into the junction and binds to complementary receptors on the sarcolemma

The wave of depolarisation travels along the sarcolemma nad down transverse tubules (T-systems)

This wave of depolarisation down the tubule excites the sarcoplasmic reticulum.

The sarcoplasmic reticulum releases calcium ions into the cytoplasm

Calcium ions are involved in two processes

o Binding to troponin

o Activating ATPase

Calcium firstly binds to troponin

Troponin shifts out of its default position and as it does so it pulls tropomyosin with it

This exposes the actin myosin binding site that is blocked when the tropomyosin is in its default position

The myosin head can now bind to the actin filament, forming a CROSS BRIDGE

Meanwhile other calcium ions have activated the enzyme ATPase which catalyses the hyfrolysis of ATP ADP + Pi releasing energy

This energy moves the myosin head at the hinge region pulling the thin actin filament over the think myosin filament = POWER STROKE

The cross bridge is stable and so ATP needs to bind to the myosin filament to provide energy to break the cross bridge

Now the cross bridge is broken the myosin head can bind to another actin-myosin binding site forming another cross bridge further along the actin filament. This only occurs if there is enough calcium ions and ATP molecules

If either ATP or calcium ions are limiting then the filaments slide back to their starting positions and the muscles relaxes

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Outline the role of ATP in muscular contraction, and how the supply of ATP is maintained in muscles.

ATP comes from three sources

o Aerobic respiration

Requires Oxygen and respiratory substrate

Produced rapidly in the many mitochondria

o Anaerobic respiration

Produced quickly in the sarcoplasm

Leads to a build up of lactic acid

Leads to an increase of blood to the muscles

o Phosphocreatine (PCr)

Donates phosphate to phosphorylate ADP ATP

Phosphocreatine

Creatine Phosphotransferase

Phosphocreatine

ADP

ATP

P

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Compare and contrast the action of synapses and neuromuscular junctions.

Neuromuscular Junction Synapse

Neuromuscular Junction Synapse

Neurotransmitter is acetylcholine Various neurotransmitters

Acetylcholinesterase breaks down neurotransmitter

Various enzymes breaks down the neurotranmitters

Between neurone and muscle Between two neurones

Post junction membrane is clefted Post synaptic membrane is smooth

Many receptors Fewer receptors

Needs one action potentials to cause depolarisation on post synaptic

membrane Needs many action potentials to cause

depolarisation on post synaptic membrane

Similarities

Both release neurotranmitter by exocytosis

Calcium ions cause vesicles to migrate and fuse with prejunction membrane

Neurotransmitter crosses synapse by diffusion

Both post junction membranes have sodium channels

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Outline the structural and functional differences between voluntary, involuntary and cardiac muscle.

Involuntary (Smooth) Muscle Cardiac Muscle Voluntary (Skeletal)

Muscle

Not Striated Striated Striated

Uninucleated Multinucleated Multinucleated

Contracts slowly Contracts quickly Contracts quickly

Fatigues slowly Does not fatigue Fatigues quickly

Unconscious control Unconscious control Conscious control

Single cells Cells branch and interlink Cells in fibres

Found in Walls of interstines, arteries, bonchioles and the iris of

the eye Found in the heart Found in muscles that

move the skeleton

spindle shaped Intercalary discs with

free ions Contain micrfibrils

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Skeletal Muscles

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Smooth Muscles

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Cardiac Muscles

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State that responses to environmental stimuli in mammals are coordinated by nervous and endocrine systems.

&

Explain how, in mammals, the ‘fight or flight’ response to environmental stimuli is coordinated by the nervous and endocrine systems.

Cerebral Cortex

Hypothalamus

Anterior Pituitary Gland

Releases CRF Corticosteroid Releasing Factor

Adrenal Cortex

Releases Adrenaline

Adrenal Gland

Releases ACTH AdrenoCorticoTropic

Hormone Glands & Smooth muscles

Iris

Gut Wall

Heart rate

Sweat

Hairs

Sympathetic pathway

Blood stream

Releases 30 different hormones

Sensory Receptors

Adrenal Medulla

Physiological Changes

Increase heart rate

Increase Ventilation

Increase Blood Glucose

Increase Sweating

Increase Pupil dilation

Dilate arterioles of the liver and muscles

Constrict arterioles of the digestive system

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Questions

1. Below is a drawing of the brain that shows the origin of the cranial nerves.

A

B

C

D

(a) State the direction from which the brain has been drawn.

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[1]

(b) (i) Name the structures A, B, C and D shown on the diagram.

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B .............................................................................................................

C .............................................................................................................

D .............................................................................................................

[4]

(ii) State two roles of structure D.

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2 .............................................................................................................

[2]

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(c) The hypothalamus constantly monitors and regulates the concentration of hormones in the blood. Outline how the hypothalamus regulates the concentration of hormones in the blood.

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[2]

[Total 9 marks]

2

Calcium ions are necessary for the contraction of rabbit’s striated muscle.

Describe the role played by calcium ions in the contraction of striated muscle.

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[Total: 3 marks]

3

The figure below shows a section through a human elbow joint.

humerus

ligament

synovial membrane

ulnaAB

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(i) Name A and B.

A ..................................................................

B ..................................................................

[2]

(ii) Describe the roles of A and B in the movement of the elbow joint.

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[3]

[Total 5 marks]

4

The cerebellum and medulla oblongata are regions of the brain. The cerebellum is concerned with the control and coordination of movement and posture.

Suggest why the cerebellum of a chimpanzee is relatively larger than the cerebellum of a cow.

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5

The figure below shows a vertical section through the human brain.

corpus callosum

thalamus

hypothalamus

pituitary body

medulla oblongata cerebellum

pineal body

cerebrum

cerebralcortex

corporaquadrigemina

Front

(i) Name the structure shown above that links the two cerebral hemispheres.

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[1]

(ii) The table below shows the functions of some areas of the brain.

Complete the table using the labels in the figure above.

area of brain example of function

....................................................... co-ordination of posture

....................................................... control of heart rate

....................................................... control of temperature regulation

....................................................... control of speech

[4]

[Total 5 marks]

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6

In this question, one mark is available for the quality of use and organisation of scientific terms.

The following figure shows a neuromuscular junction.

synaptic cleft

post-synaptic

membrane

myofibril

mitochondrionmotor

neurone

pre-synaptic

membrane

The figure above shows that mitochondria are present on both sides of the synaptic cleft. Explain why mitochondria are essential for the transmission of impulses across the cleft and for muscular contraction.

transmission of impulses across the cleft .................................................................

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muscular contraction ................................................................................................

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[8]

Quality of Written Communication [1]

[Total 9 marks] 7

(a) The cerebellum and medulla oblongata are both parts of the hindbrain. Outline the functions of these two parts of the brain.

cerebellum

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[2]

medulla oblongata

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(b) Alzheimer’s disease is characterised by several changes in the cerebrum, including ‘tangles’ inside neurones and ‘plaques’ between neurones.

State what causes

(i) tangles; ..................................................................................................

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(ii) plaques. .................................................................................................

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[2]

Another change in the cerebrum of a person with Alzheimer’s disease is a decrease in acetylcholine released by neurones that form memory circuits.

During a clinical trial, people with Alzheimer’s disease were treated with a drug that inhibited the enzyme acetylcholinesterase. This improved their short-term memory.

(c) Suggest how the drug may inhibit acetylcholinesterase.

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[3]

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(d) Suggest how the drug improves short-term memory.

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[2]

(e) State three precautions that should be taken when designing such clinical trials, to ensure that any effects are due to the drugs being tested.

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[3]

[Total 14 marks]