Animal Responses

The Cerebrum

• Largest part of brain - divided into two hemispheres connected by the corpus collosum
• beneath surface is the cerebral cortex  - responsible for speech, emotions and decision making
• cerebral cortex subdivided into sensory areas, association areas and motor areas 
• impulses from ears, eyes and sense organs arrive at association areas 
• in motor areas nerve impulses are sent to effectors

Cerebellum - Controls the coordiantion of movement and posture

• Recieves impulses from ears, eyes and stretch receptors in muscles and other parts of the brain
• Information is intergrated and used to coordinate the timing and pattern of skeletal muscle and contraction and relaxation. 

Medulla Oblongata - controls autonomic nervous system

• Controls involuntary movements eg breathing and heartbeat 

Hypothalamus - regulates the autonomic nervous system

• also controls the secretion of hormones from the pituitary gland 
• controls many homeostatic processes eg temperature regulation and water content of body fluids

Central Nervous System - 

• brain and spinal cord 
• made of grey matter (non-myelinated nerve cells) and white matter (myelinated nerve cells)
• most cells are intermediate neurons  - short dendrites forming synapses with other cells
• spinal cord extends from base of brain - cerebro-spinal fluid flows through the centre
• meniges surround the brain and spinal cord - secrete cerebro-spinal fluid which absorbs mechanical shock and provides nutrients and oxygen to brain cells

Peripheral Nervous System 

• Neurons that carry impulses in and out of the CNS - sensory neurons carry impulses from receptors and motor neurons carry impulses to effectors
• sensory neuron cell bodies just outside spinal cord in dorsal root ganglia 
• made of two systems - somatic and autonomic nervous system
• somatic nervous system includes sensory neurons and motor neurons that take information to skeletal muscles
• sensory neurones lie just outside in the spinal cord in dorsal root gsnglia

Somatic Nervous System 

• somatic nervous system includes sensory neurons and motor neurons that take information to skeletal muscles - under voluntary control

Autonomic Nervous System

• carries action potentials to internal organs - viscera, and smooth muscle 
• self governing  - operates independly of concious control - involunatry
• controls cardiac muscle and activities of exocrine glands
• motor neurons have cell bodies outside of CNS in autonomic ganglia - preganglionic neurone carries action potentials from CNS to autonomic ganglion
• autonomic nervous system divivided into sympathetic and parasympathetic nervous system

Sympathetic Nervous System 

• From autonomic ganglia, axons pass to all organs in the body and form synapses with the muscle - transmitter substance is usually noradrenaline, which stimulates the tissue eg heart beats faster
• Also stimulate the adrenal glands causing them to secrete adrenaline and noradrenaline
• Brings about changes such as speeding up the heart rate, dialation of pupils, dialation of arteriolds

Parasympathetic Nervous System

• All nerve pathways begin in the brain, top of spinal cord or bottom of spinal cord
• Neurons go straight from there start location to the effector, and dont pass through an autonomic ganglia
• many axons are in the vagus nerve - the neurotransmitter is acetylcholine, which has an inhibitor effect 

Muscles are made of cells that are enlongated to form fibres 

Involuntary (Smooth Muscle)

• under control of the autonomic nervous system
• does not look stripy - said to be non-straited
• made of individual cells with their own nucleus - cells are long and thin (400um by 5um wide)
• found in walls of arteries/arteriolds, iris of the eye and walls of intestine
• contraction caused by sliding of actin and myosin but are not arranged to form myofibrils or sarcomeres
• contraction intiated by action potential along autonomic nervous system or by hormones such as adrenaline

Cardiac Muscle

• only found in the heart 
• straited, each cell containing fibrils made up or sarcomeres 
• cells are smaller than skeletal muscle cells - each cell has one nucleus also
• cells branch and form connections with adjacent cells
• have more mitochondria 
• have a contiunous supply of oxygen in order to perform continuous work
• uses fatty acids rather than glucose as respiratory substrate

Skeletal Muscle (Voluntary)

• Action leads to movement of skeleton 
• cells contain several nuclei - syncitium
• cells surrounded by cell surface membrane called sarcolemma - muscle cell cytoplasm known as sarcoplasm 
• plasma membrane has infolds in the interior known as T tubules
• sarcoplasm contains many mitochondria, sarcoplasmic reticullum (specialised endoplasmic reticulum) and myofibrils 
• myofibrils are the contractile elements and consist of sarcomeres - two types of protein myofilaments - thin actin and think myosin
• darker areas (A bands) are where the myosin is, lighter areas (I Bands) is where the actin is
• Z line provides attachment of actin filaments whereas M lines provide attachment for myosin
• between two Z lines is called a sarcomere
• fatigues quickly

Myosin

• Myosin is a fibrous protein which has a tail attached to the M line and two heads
• severall myosin molecules lie in a bindle, making a myosin filament

Actin

• Actin is a globular protein but many together form a chain
• two of these chains twist together to form an actin molecule
• Tropomyosin twists around actin chains
• Troponin attaches to the actin chain at regular intervals

The Power Stroke

• Troponin and tropomysoin molecules change shape and move to different positions on actin exposing the binding site for myosin - myosin head binds to actin forming a cross-bridge
• Myosin heads tilt pulling the actin filaments 
• The heads then hydolyse ATP making them release the actin and moveback, and bind again
• They tilt again pulling the actin further - this process can repeat aslong as the binding site is not blocked and if the muscle has enough ATP
• The shortening of the sarcomere shortens the whole length of the muscle, known as contraction

• Action potential arrives at end of motor neurone and acetylcholine diffuses across the synaptic cleft
• Sarcolemma acts as post synaptic membrane and acetylcholine binds to the membrane, depolarising it and generating an action potential
• the action potential travels down T tubules where its picked up by the sarcoplasmic reticullum - calcium ions are pumped in by active transport
• action potential stops active transport and calcium ion channels open releasing calcium ions into the sarcoplasm
• calcium binds to troponin molecules, causing troponin and tropomyosin to change shape and move, exposing the myosin heads binding site, ready for a cross bridge to be formed and muscle contraction to begin

ATP Supply

• Muscles have a small store of ATP but this is very minute
• Creatine phosphate used after the small ATP reserves have been used
• A phosphate is removed from creatine phosphate and used to regenerate ATP from ADP - enzyme creatine phosphotransferase is used
• ATP can be supplied via respiration after this - either aerobically or anaerobically