Responding to the environment (Pt2) Bio
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Imagine the gross structure of the brain. (Btw, the 'cerebral cortext' in the diagram should be 'cerebral cortex'. (Also, the hypothalamus in the diagram should be closer to pituitary gland).
Describe the cerebrum.
- Largest part of the brain, folded, and divided into two hemispheres connected by the corpus callosum. (This region of brain is more highly developed in humans than in any other organism).
- Cerebral cortex is think layer of cells bodies on the outer layer of cerebrum.
Outline the functions of the cerebrum/cerebral cortex.
- In control of the 'higher brain functions' such as conscious thought and emotion, ability to override some reflexes, and intelligence, such as reasoning, judgement and language. This makes us human.
- Also involved in vision, hearing and using these information to coordinate response.
The cerebral cortex is ___, for reference, into areas responsible for specific activites and body regions. What are they?
- Sensory areas: receive impulses indirectly from receptors.
- Association areas: compare input with previous experiences in order to interpret what the input means and judge appropriate response.
- Motor areas: send impulses to effectors (muscles and glands).
- Left and right side: Left side control muscular movements on right side of body and vice versa.
Describe the cerebellum and its function.
- Underneath cerebrum and also has a folded cortex - and has half of all nerve cells in the brain.
- Key role in muscle coordination (and fine movement) and coordination of balance and posture.
- It processes sensory information from the retina, balance organs in the inner ear, specialised muscle fibres called sindle fibres and the joints.
- Neurones from the cerebellum carry impulses to the motor areas so that motor output to the effectors can be adjusted to the requirements. We can often go on 'auto-pilot'.
Describe the medulla oblongata and its function.
- Found at base of brain, at the top of spinal cord.
- Controls action of smooth muscle in gut wall, breathing movements and heart rate. Regulatory centres including;
- Cardiac centre - control heart rate
- Respiratory centre - control breathing (depth and rate).
Describe the hypothalamus and its function.
- Found just beneath the middle part of brain, very close to pituitary gland.
- Controls most of body's homeostatic mechanisms. And autonomic nervous system.
- Sensory input from temp receptors and osmoreceptors received by hypothalamus and leads to negative feedback mechanism. (eg. for body temp and blood water potential).
- Also control much of endocrine function of body because it regulates pituitary gland.
The CNS (__ and ___ ___) receives ___ information and coordinates an appropriate ___. The ___ passes on ___ information to the ___ area in __ __, to create ____ muscular movement. If response needed is ___, then ___ sends signals along neurones to stimulate ___ muscles to ___.
- brain and spinal cord
- cerebral cortex
Animals need to respond to their __ and __ environments in order to ___ its chance of ___. Any change in these environment is called a ___.
- internal and external
- increase its change of survival
Describe the two subdivisions of the nervous system.
- Central nervous system (CNS): consists of brain and spinal cord. Made of grey matter (non-myelinated nerve cells) and white matter (longer, myelinated axons and dendrons that carry impulses).
- Peripheral nervous system: connects the CNS to the rest of the body.
Further divide the motor systems in the peripheral nervous system into 2 divisions.
- Somatic motor neurones: carry impulses from DNA to skeletal muscles which are under voluntary control.
- Autonomic motor neurones: carry impulses from CNS to involuntary muscles and glands - eg. smooth muscle in gut wall, cardiac muscle, glands.
Further divide the autonomic nervous system into 2 divisions. How can we describe these two systems?
- Sympathetic nervous system: Gets the body ready for action - the 'flight or fight' system. Sympathetic neurones release noradrenaline. Eg. increased heart rate, pupil dilation.
- Also, neurones of a pathway are linked at a ganglion just outside the spinal cord - so pre-ganglionic neurones are very short.
- Parasympathetic nervous system: Calms the body and down and let it rest and digest. Parasympathetic neurones release neurotransmitter acetylcholine. Eg. decrease heart rate, pupil constriction.
- The neurones of a parasympathetic pathway are linked at a ganglion within the target tissue. So pre-ganglionic neurones vary considerably in length.
- Can be described as antagonistic systems
- [Also important to remember that under normal conditions, impulses passing along at low rate - only when there's a change there's an altered balance of stimulation between the two systems.]
Voluntary muscles are attached to the bones of skeleton by ___ (1), such that contraction of the muscles move the bones at the ___. What is (1)?
- tendons - made of tough inelastic collagen
In a joint, there is at least two muscles that are described as ___ __. Why? Also, when groups of muscles control they are called ___(2).
- antagonistic pairs
- Because muscles are only capable of producing a force when they contract. So movement of any bone at joint requires coordinated action of at least two muscles.
- As one muscle contracts, the other of the pair must relax to allow for smooth movement.
- synergists (2) (CHECK)
What is a: 1) Tendon; 2) Ligament; 3) Cartilage; 4) synovial fluid. + Where is the synovial fluid produced?
- 1) Attach muscles to bones
- 2) Attach bones to other bones, hold them together to prevent dislocation.
- 3) Pads where bones meet to reduce friction as the bones move.
- 4) A lubricant at a joint. It eases the movement of the bones at the joint.
- Synovial fluid surrounded/produced by synovial membrane.
Give 3 different types of joints. And an example for each.
- Ball and socket joints: allow movement in all directions. Eg. shoulder
- Gliding joints: allow wide range of movement because small bones slide over each other. Eg. wrist
- Hinge joints: allow movement in one plane only, like up and down. Eg. elbow
Imagine the bones and the muscles and the other stuff that is involved in the movement of the elbow joint.
When your __ contracts, your ___ relaxes. This pulls the bone so your arm bends at the ___. When your ___ contracts, your ___ relaxes. This pulls the bone so your arm ___ at the ___.
Remember that when a motor neurone connects to muscle cell/fibre, they connect at ___ __, not ___.
- neuromuscular junction
How are strengths of muscular contraction controlled? (Maybe don't need to know - as it is also to do with frequency of nerve impulse and summation etc).
- Brain controls the strength of contraction because many motor neurones stimulate a single muscle.
- Each motor neurone branches to neuromuscular junctions, causing contraction of cluster of muscle cells, known as a motor unit. The more of these stimulated, the greater force of contraction.
- Known as gradation of response.
Briefly outline the steps after the transmitter substances are released into the synaptic cleft in a neuromuscular junction and how this makes the muscle contract.
- 1. Acetylcholine bind with receptors in sarcolemma (plasma membrane), causing them to open Na+
- 2. Na+ floods in and depolarises membrane and intiates action potential, which spreads along membrane.
- 3. Depolarisation of sarcolemma spreads down T-tubules.
- 4. Ca2+ channels open and Ca2+ ions diffuse out of sarcoplasmic reticulum.
- 5. The Ca2+ cause contraction in muscle. (will be covered later, but Ca2+ ions bind to troponin. Tropomyosin moves to expose myosin binding sites on the actin filaments. Myosin heads bind and filaments slide).
Compare and contrast synapses and neuromuscular junctions. (4&5)
- Similarities: In both, arrival of action potential causes calcium ion channels in the plasma membrane of presynaptic neurone, so calcium ions flood into cytoplasm,
- causing vesicles containing transmitter substance to fuse with presynaptic membrane and release the substance.
- This causes depolarisation of postsynaptic membrane, in both cases.
- Also, enzymes present to break down neurotransmitter to avoid continual stimulation.
- At neuromuscular junction, action potential in muscle fibre is carried deep into cell along T-tubules, eventually affecting the sarcoplasmic reticulum. Does not happen in synapse.
- Neurotransmitter in neuromuscular junction is acetylecholine. In synapses, there are various transmitters, not just acetylcholine (eg. dopamine).
- In n.m.junction, post-synaptic membrane is plasma membrane (sarcolema) of muscle cell/fibre, but in synapses, it is the plasma membrane of another neurone.
- in n.m.junction, muscle cell always contracts, whereas in synapses, action potential may or may not fire in next neurone. (CHECK!)
- In n.m.junction, postsynaptic receptor is nicotinic cholinergic receptors, whereas in synapses it varies.
Muscles are composed of cells that are ___ to form ___. They are able to ___ and ___. All muscles produce a force on ___ because they contain __ made of the proteins __ and ___.
List the 3 types of muscle we need to know about and know the differeces between.
- Involuntary muscle - also known as smooth muscle.
- Cardiac muscle
- Voluntary muscle - also known as striated or skeletal muscle.
Describe the structure of voluntary muscle.
- Muscle cells form fibres. Diameter about 100um (micrometres), length could be many centimetres.
- Each cell/fibre is multinucleate - has several nuclei.
- It is striated - shows a striped/banded pattern, because of the different bands in the muscle fibre/and myosin.
Describe the function of a voluntary muscle.
- Contraction of these lead to movement of the skeleton at the joints, and is controlled consciously, hence 'voluntary' muscles.
- They contract quickly and powerfully
- But it fatigues quickly, unlike involuntary and cardiac muscle.
- (Some voluntary muscles contract slowly and fatigue slowly - usually involved in endurance and posture).
Outline the structure of involuntary muscle, trying to compare with the 2 other types throughout as much as possible.
- Are not striated like voluntary or cardiac muscle. (hence 'smooth muscle')
- Muscle cells are 'spindle-shaped'.
- As in other muscles, the contraction is cause by sliding of acting and myosin filaments, but these are not arranged to form myofibrils or sarcomeres.
- A single nucleus, like cardiac muscle, but unlike voluntary muscle.
- Cells are about 400um long and 5um wide and lie parallel to each other.
How does smooth muscle contract, and what are its functions? Give examples at the end of one place where it functions.
- It is not under voluntary control. Smooth muscle is innervated by neurones of the autonomic nervous system.
- Contraction can be initiated by autonomic nervous system or by hormes such as adrenaline.
- They contract more slowly and steadily than other types of muscle, and fatigues very slowly.
- Eg. Walls of intestines - peristalsis. Caused by longitudinal (wave-like contractions) and circular layer (contraction causes segmentation).
Describe the structure of cardiac muscle and its function/way it contracts.
- The muscle cells (shaped like cylinders o.2mm long) form branched fibres to allow impulses to spread quickly through the whole muscle.
- Intercalated discs (membranes with small gap junctions with free diffusion of ions so action potential pass very easily between fibres) join cells at their ends.
- Also more mitochondria than skeletal muscles. And respires fatty acids, not glucose.
- Each muscle cell/fibre has one nucleus, like involuntary muscle.
- They are striated (like voluntary), but pattern isn't as strong as in voluntary.
- Cardiac muscle is myogenic - contracts without nerve impulse, but rate controlled involuntarily by autonomic nervous system).
- Contract fast and rhythmically, but do not fatigue.
IMPORTANT. Ok, so we looked at all the different types of muscle. Now, just to make it clear in one flashcards, compare all of them for structure and function. (5)
- Involuntary: short, spindle-shaped cells, each with single nucleus. Voluntary: Cells form long multinucleate fibres. Cardiac: Cells form branched fibres with intercalated discs joining cells at their ends.
- I: Unstriated appearance under microscope. V: Striated appearance under microscope. C: Striated appearance under microscope.
- I: Contracts slowly & fatigues slowly. V: Contracts quickly & fatigues quickly. C: Contracts quickly but does not fatigue.
- I: Contraction is under autonomic nervous system control V: Under voluntary nervous system control. C: Myogenic. Autonomic nervous system controls the rate of contraction.
- I: Involved in movement of materials along internal tubes, such as gut. Involved in autonomic reflexes such as pupil dilation. V: Voluntary movements of the bones about joints. C: Pumping blood around body.
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