Animal responses

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The brain

Cerebrum: divided into two hemispheres, joined by the corpus callosum and consists of the cerebral cortex (layer of nerve cell bodies). It deals with the 'higher functions', eg. conscious thought and emotional responses, the ability to override some reflexes and features associated with intelligence such as reasoning and judgement. 

Cerebral cortex split into:
-sensory areas- receive impulses indirectly from the receptors
-association areas- compare input with previous experiences in order to produce an appropiate response 
-motor areas- send impulses to effectors (muscles and glands)


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The brain

Medulla oblongata: Controls non-skeletal muscles (cardiac and involuntary muscles), and is in control of the autonomic nervous system. It controls the regulation of the respiratory centre-controls breathing and regulates the rate and depth of breathing. Also regulates cardiac centre-regulating heart rate. 
Hypothalamus: Sensory input from thermoreceptors and osmoreceptors leads to automatic responses that regulate body temp and blood water potential. Also controls endocrine function because it regulates pituitary gland. 

Coordinated motor responses eg:
-muscular activites in responding to changes in body position to remain balanced and upright
-sensory activites e.g judging position of objects and limbs
-tensioning of muscles in order to manipulate tools effectively
-operation of antagonistic muscles- contraction/relaxation

Neurones from the cerebellum carry impulses to these motor areas-it plays a big role in coordinating balance and fine movement. to do this, it processes sensory info from: the retina, the balance organs in the ear, spindle fibres and the joints

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Organising the nervous system

Nervous system:- C.N.S (central nervous system) MADE OF BRAIN AND SPINAL CORD 

Peripheral N.S (neurones that connect CNS to the rest of body

Peripheral N.S.--- sensory (neurones that carry impulses from receptors to CNS (cell bodies outside CNS in dorsal root ganglions) + Motor (neurones that carry impulse from CNS to effector, cell bodies IN CNS)

Sensory- Somatic NS (skeletal muscles under volntary control)

Motor- Autonomic NS (controls unconscious activites eg digestion and heart rate 

Autonomic NS- Sympathetic - prepares body for fight/flight - release NT noraadrenaline

Parasympathetic - rest/digest system - neurones release NT acetylcholine

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Autonomic Nervous System

  • Controls homeostatic mechanisms+stress response 
  • Neurons mostly non-myelinated (myelinated in somatic NS)
  • connections to effectors usually consisting of at least 2 neurones that join to make a ganglion-somatic NS only has one neuron.
  • short, pre-ganglionic neurones + long post ganglionic neurones
  • -produces fight or flight response
  • -increased breathing rate
  • -increased heart rate
  • -dilated pupil
  • -******
  • -long pre-ganglionic neurones+short post ganglionic neurones +rest/digest
  • -decreased heart rate
  • -decreased breathing rate
  • -constricted pupil
  • -sexual arousal
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Coordinated movement

The elbow joint is an example of a synovial joint - they require a large amount of movement- the synovial fluid is the lubricant- eases the movement at the joint. The biceps and triceps muscles act antagonistically in order to move the forearm at the elbow.

1- Impulses arriving at the neuromuscular junction cause vesicles to fuse with the pre-synaptic membrane and release acetylcholine into the gap

2- Acetylcholine binds to receptors on the muscle fibre membrane (sarcolemma) causing depolarisation

3- Depolarisation wave travels down tubules (T system)

4- T system depolarisation leads to calcium release from stores in the sarcoplasmic reticulum 

5- Calcium binds to proteins in the muscle, which leads to contraction

6- Acetylcholinesterase in the gap rapidly breaks down acetylcholine so that contraction only occurs when impulses arrive continuously.

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Coordinated movement

Neuromuscular junction: specialised synapse which occurs at the end of a motor neurone where it meets the muscle fibre. Release of acetylcholine, following depolarisation at the neuromuscular junction, stimualtes contraction of the muscle fibre

The motor unit:
-Some muscular movemtns require stornger contraction- the brain controls the strength of contraction because many motor neurones stimulate a single muscle. Each one branches to neuromuscular junctions, causing the contraction of a cluster of muscle cells- known as a motor unit. The more motor units stimulated=greater the force of contraction. This is GRADATION OF RESPONSE. 

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Three Types of Muscle

Three types= voluntary (striated/skeletal), involunatary (smooth muscle), cardiac muscle 

Involunary muscle: 
e.g. walls of the intestine- circular and longitudinal bundles - peristalsis - moves food along the intestine

iris of the eye -  circular and radial bundles - controls the intensity of light entering the eye - contraction of radial muscles dilates the pupil, contraction of circular muscle constricts the muscle 

wall of arteries, arterials and cervix - circular bundles - regulation of blood press+redirecting blood to voluntary muscles during exercise 
-contraction of muscle narrows vessel diameter so reducing blood flow 
-relxation causes dilation=increased blood flow 

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Three types of muscle

Cardiac muscle:

-arterial muscle
-ventricular muscle
-specialised excitatory and conductive muscle fibres 

Myogenic but rate is controlled by the Autonomic NS. The muscle fibres are a cylindrical shape with limited striation. The muscle fibres have intercalculated discs which have low electrical resistance so impluses can pass easily between cells. The muscle fibres are branched so impulses can spread even quicker! The muscles contract rhythmically and dont fatigue. 

Voluntary (skeletal/striated muscle) :
The action of voluntary muscles =movement of the skeleton at joints.
Muscle cells form fibre of about 100um in diameter containing nuclei-each fibre is surrounded by a membrane (sarcolemma). Muscle cell cytoplasm = sarcoplasm and has organelles eg mitochondria, sarcoplasmic reticulum and myofibrils called sarcomeres containing myosin and actin. 

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Sliding Filament Model!

The sarcomere: Z line to Z line= sarcomere- when relaxed 2.5 nanometres long/ Z band reduces when contraction occurs because I band and H zone reduce- A band does not change length. 

Two types of protein filament involved:

Thin filaments= actin- coiled around eachother like a twisted double string of beads each strand made of G actin subunits (globular). Tropomyosin (rod shaped protein) coil around the F actin. A troponin molecule is attached to each tropomyosin molecule consisting of 3 polypeptides- one binds to actin, one to tropomyosin to keep it in place around the actin filaments and one around calcium ions.

Thick filaments are bundles of myosin-each molecule has 2 heads and a tail- each filament contains many myosin molecules whose heads stick out from opposite ends of the filament. 

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Sliding Filament model!

The Power Stroke:
1) Myosin head groups attach to the surrouding actin filaments forming a CROSS BRIDGE

2) The head group then bends causing the thin filament to be pulled along and so overlap more w the thick filament. This is the POWER STROKE where ADP+P(i) is released

3) The cross bridge is then broken as new ATP attaches to the myosin head 

4) The head group moves backwards as the ATP is hydrolysed to ADP+P(i). It can then form cross bridge w the actin filament further along and bend again (2). 

The calcium ions that are released by the sarcoplasmic reticulum cause the troponin to change shape, and the actin myosin binding sites are uncovred and so cross bridges can form=power stroke and muscle contraction. When stimulation stops, calcium ions are actively transported back into the sarcoplasmic reticulum by carrier proteins = RELAXATION. 

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Sliding Filament Model!

ATP: ATP is required to break the cross bridge connection and re-set the myosin head backwards further along to the next binding site along the actin molecule. 

Maintenance of ATP supply:
-In order for continuous contraction to happen, there must be a continuous supply of ATP. Achieved in 3 ways:
--> Aerobic respiration in muscle cell mitochondria
-->Anaerobic respiration in muscle cell sarcoplasm: build up of lactic acid in muscles which stimulates increased blood supply to muscles
-->Transfer from creatine phosphate in the muscle cell sarcoplasm: phosphate group from creatine phsophate can be used to turn ADP into ATP by the enzyme creatine phosphotranferase. 

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Environmental stimuli+fight/flight

Environmental stimuli are coordinated by the endocrine and nervous systems.

Fight or flight physiological response:
-increased heart and breathin rate
increased blood glucose levels
-dilated pupils
-increased sweat production

-Sympathetic nervous system triggers release of adrenaline frm adrenal medulla into blood 
-Hypothalamus releases corticotropin releasing factor (CRF) into pituitary gland, which releases ACTH into blood causing 30+hormones to be released from adrenal cortex 
-they resist stressors

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