F215 Module 4 The Brain and Muscles

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  • Created by: Lexi
  • Created on: 08-02-13 12:00
What is the cerebrum?
It is the largest, most recognisable part of the brain. It is responsible for the elements of the nervouse system that are associated with being 'human' including though, imagination and reasoning
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What are the names of the 'halves' of the brain?
The left and right cerebral hemispheres
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What is the outermost layer of the cerebrum known as?
The cerebral cortex
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What does the cerebral cortex control?
Higher brain functions such as concious thought, emotional responses, the ability to override some reflexes and features associated with intelligence like reasoning and judgement
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What connects the two hemispheres of the brain?
The corpus callosum
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How is the cerebral cortex subdivided?
Into sensory areas, association areas and motor areas
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What do sensory areas do?
Receive impulses indirectly from the receptors
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What do association areas do?
Compare input with previous experiences in order to interpret what the input means and judge an appropriate response
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What do motor areas do?
Send impulses to effectors (muscles and glands)
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What do the motor areas on the left side of the cerebral cortex control?
The muscular movements on the right side of the body
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What does the cerebellum control?
The coordination of movements and posture
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What does the hypothalamus control?
The autonomic nervous system and the endocrine glands i.e. most of the body's homeostatic mechanisms
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What does the medulla oblongata control?
The action of smooth muslce in the gut wall, and controls breathing movements and heart rate
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Who is Broca's area named after and what did he do?
Paul Broca worked in the 1860s examining patients with aphasia (inability to speak)
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Who is Wernicke's area named after and what did he do?
Karl Wernicke worked in the 1860s to identify another region, damage to which caused problems understanding language
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Why do animals need to be able to respond to their internal and external environments?
So that they are able to survive e.g. run away from predators, control their internal temperature etc
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Wha is the CNS? Describe it
Central Nervous System. It consists of the brain and spinal cord, and is made up of grey and white matter
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What is the difference between grey and white matter?
Grey matter is billions of non-myelinated nerve cells whilst white matter is made up of longer, myelinated neurones
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What is the PNS?
Peripheral Nervous System
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Which neurones carry impulses from the body, to the CNS?
Sensory neurones
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Which neurones carry impulses from the CNS, to the effectors?
Motor neurones
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How is the motor system subdivided?
Into somatic and autonomic neurones
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What do somatic motor neurones do?
Carry impulses from the CNS to skeletal muscles, which are under concious control
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What do autonomic motor neurones do?
Carry impulses from the CNS to cardiac muscle, to smooth muscle in the gut wall and to glands, none of which are under concious control
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How is the autonomic nervous system sub-divided?
Into sympathetic and parasympathetic
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Are most autonomic neurones myelinated or non-myelinated?
Non-myelinated
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How do autonomic and somatic connections to effectors differ?
Autonomic connections consist of at least 2 neurones, which connect at a ganglion. Somatic connections only have 1 neurone
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Why are the sympathetic and parasympathetic systems known as antagonistic?
Because generally the action of one system opposes the action of the other
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When is the parasympathetic system most active?
In sleep and relaxation
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When is the sympathetic system most active?
In times of stress
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How long are pre-ganglionic nerves in the parasympathetic nervous system?
The neurones of a pathway are linked at a ganglion within the target tissue, so they cary considerably in length
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How long are pre-ganglionic nerves in the sympathetic nervous system?
The neurones are linked at a ganglion just outside the spinal cord, so they are very short
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What substances do the sympathetic and parasympathetic post-ganglionic neurones secrete at synapses between neurones and their effectors?
The parasympathetic secretes acetylcholine whilst the sympathetic secretes noradrenaline
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Describe the effects of parasympathetic action
Decreased heart rate, pupil constriction, decreased ventilation rate
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Describe the effects of sympathetic action
Increased heart rate, pupil dilation, increased ventilation rate
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How are voluntary muscles attached to bones?
By tendons
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What are tendons?
Tough, inelastic collagen which is continuous with the muscle and the periosteum
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What are the periosteum?
Connective tissues convering the bone
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How are muscles working in pairs opposite each other described?
Antagonistic
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The movement of bones at many joints require a wide range of actions, and are under the control of groups of muscles called...?
Synergists
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Give an example of a synovial joint
The elbow
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Why is there synovial fluid at the joints?
To act as a lubricant, easing the movement of the bones at the joint
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What is the 'synapse' between a motor neurone and a muscle called?
A neuromuscular junction
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What is the neurotransmitter used at neuromuscular junctions called?
Acetylcholine
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What is the name for the muscle fibre membrane after the neuromuscular junction?
The sarcolemma
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What happens after acetylcholine binds to receptors on the sarcolemma?
A depolarisation wave travels down tubules, called the T system
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What does T system depolarisation lead to?
Ca2+ ions being released from stores in the sarcoplasmic reticulum
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What is sarcoplasmic reticulum?
Specialised endoplasmic reticulum
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What do the calcium ions do?
Bind to proteins in the muscle, leading to contraction
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How is it ensured that contraction only occurs when impulses arrive continuously?
Acetylcholinerase in the gap rapidly breaks down the acetylcholine
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There is a process which allows the brain to control the muscles' strength of contraction, stimulating different numbers of motor units. What is this called?
Gradation of response
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Name the 3 types of muscle
Voluntary (or skeletal/striated), Involuntary (or smooth) and Cardiac
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Why are smooth muscle contractions not under conscious control?
Because smooth muscle is innervated by neurones of the autonomic nervous system
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Describe the action and arrangement of muscle cells in the walls of the intestine
The smooth muscle is made up of circular and longitudinal bundles, and it's action is known as peristalsis (moves food along intestines)
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Describe the action and arrangement of muscle cells in the iris of the eye
The smooth muscle is made up of circular and radial bundles, and they control the intensity of the light entering the eye
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Describe smoot/involuntary muscle cells
Spindle shaped, containing bundles of actin and myosin with a single nucleus. Relaxed cells are about 500 um long and 5 um wide
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Are contraction and fatigue slow or fast in involuntary/smooth muscle cells?
Slow
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Name the 3 types of cardiac muscle
Atrial, Ventricular, Specialised excitatory and conductive muscle fibres
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How do atrial and ventricular muscles contract?
Like skeletal muscles but with a longer period of contraction
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What is 'myogenic contraction'?
Where some cardiac muscle fibres are capable of stimulating contraction without a nerve impulse
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Is cardiac muscle monitored by the autonomic or somatic nervous system?
Autonomic
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What does the sinoatrial node do and what is it made of?
Made of specialised excitatory and conductive fibres. It can generate electrical activity, which spreads into the atria then the ventricles
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Is cardiac muscle striated?
Yes
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What are intercalated discs and what do they do?
Cell membranes which fuse to create gap junctions with free ion diffusion so action potentials pass through very quickly
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Does cardiac muscle fatigue?
No
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What does the action of voluntary muscle lead to?
The movement of the skeleton at the joints
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Skeletal muscle forms fibres - describe them
They are about 100 um in diameter, and contain several nuclei. Each fibre is surrounded by a membrane called the sarcolemma
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What is muscle cell cytoplasm known as?
Sarcoplasm
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Name 3 things that sarcoplasm contains
Mitochondria, an extensive sarcoplasmic reticulum, myofibrils
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What are myofibrils?
Contractile elements, consisting of a chain of smaller contractile units called sarcomeres
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What is a sarcomere?
The smallest contractile unit, or the distance from one Z line to the next
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Which band does not change length during contraction?
The A Band
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Describe the structure of the thin filaments in muscle cells
Two strands of actin twisted together, strengthened by tropomyosin (which is made up of 3x polypeptides)
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Describe the structure of the thick filaments in muscle cells
Myosin molecules attached heads to tail - each on has two heads and one tail. Each filament has many myosin molecules
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What happens in the first stage of muscle contraction?
Myosin head groups attach to the surrounding actin filaments by forming a cross bridge
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What happens in the second stage of muscle contraction?
The head group bends, causing the thin filament to be pulled along and so overlap more with the thick filament. ADP and Pi are released.
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What is the second stage of muscle contraction called?
The power stroke
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What happens in the 3rd stage of muscle contraction?
The cross bridge is then broken as new ATP attaches to the myosin head
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What happens in the 4th stage of muscle contraction?
The head group moves backwards as the ATP is hydrolysed to ADP and Pi. it can then form a cross-bridge with the next actin molecule (1) and bend again (2)
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What are the binding sites for the myosin head group on each actin fibre covered by?
Tropomyosin subunits
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What does the presence of tropomyosin do?
Means that a myosin head group cannot attach to any binding sites, cross bridges cannot form, and muscle contraction cannot occur
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What happens when an action potential arrives at a neuromuscular junction?
Calcium ions are released from the sarcoplasmic reticulum. They diffuse through the sarcoplasm and bind to the troponin molecules
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What does binding with calcium ions do to the troponin?
Changes it's shape, moving the tropomyosin away from the binding sites on the actin, so cross bridges can form so the power stroke and muscle contraction can occur
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What happens to the calcium ions when nervous stimulation stops?
They are actively transported back into the sarcoplasmic reticulum by carrier proteins on the membrane, leading to muscle relaxation
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How much ATP is available in a muscle fibre?
Enough to support 1-2 seconds of contraction only
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Name the 3 mechanisms in which ATP is regenerated to allow continuous muscle contraction
Aerobic respiration, Anaerobic respiration, Transfer from creatine phosphate in the muscle cell sarcoplasm
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How does transfer from creatine phosphate work?
CP's phosphate group can be transferred to ADP to form ATP by the action of creatine phosphotrnasferase
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What are the responses to environmental stimuli coordinated by in mammals?
The nervous and endocrine systems
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What initially happens in the brain when a fight-or-flight instinct is stimulated?
The cerebral understanding of a threat activates the hypothalamus which stimulates increased activity in the sympathetic nervous system
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What does increased activity in the sympathetic nervous system do?
Triggers the release of the hormone adrenaline from the adrenal medulla into the blood
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Aside from causing the release of adrenaline, what else does the hypothalamus do under stress?
Released CRF into the pituitary gland, stimulating ACTH release from the anterior pituitary gland
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What do CRF and ACTH stand for?
Corticotropin-releasing factor and adreno-corticotropic hormone
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What does the release of ACTH do?
Stimulates the release of many corticosteroid hormones from the adrenal cortex, some of which help the body to resist stressors
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What is a stressor?
A stimulus that causes the stress response. It causes wear and tear on the body's physical and mental resources
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Card 5

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