animal responses Flashcards
The mammalian nervous system
Made up of the peripheral nervous system (PNS) and then central nervous system (CNS).
• PNS - includes the receptors, sensory and motor neurones
• CNS - is the coordination centres, such as the brain and spinal cord.
The nervous system is also categorised into the autonomic or the somatic nervous system.
• The autonomic nervous system works constantly, subconsciously. This includes activities such as digestion, which you have no conscious control over.
• The somatic nervous system is consciously controlled. This is voluntary and is when you decide to move, for example choosing to stand up.
The human brain
The human brains is made up of billions of neurones and coordinates responses.
The key structures are the cerebrum, cerebellum, medulla oblongata, hypothalamus and the pituitary gland.
The brain
• Cerebrum - this is the largest part of the brain. The outer layer is known as the cerebral cortex. It is made up of many folds and is split into two hemispheres. The functions range from controlling conscious thoughts, language, intelligence, personality, high-level functions and memory.
• Cerebellum - This structure looks like a mini cauliflower. It is responsible for coordinating movement, muscles and balance.
• Medulla Oblongata - This is above the spinal cord. It is the centre of control for unconscious activities, such as breathing and heart rate.
• Hypothalamus - This small part of brain is responsible for homeostasis, such as temperature and water balance.
• Pituitary Gland - A small lobed structure known as the master gland because it secretes many hormones to coordinate several responses such as the ostrous cycle and osmoregulation.
responses and reflexes
A reflex is a rapid, automatic response to protect you from danger.
A reflex arc is made up of three-neurones.
• Synapses slow down responses as electrical energy is converted to chemicals that diffuse across the synapse-only two synapses in the process, therefore rapid.
• As no conscious decision is involved, the response is also rapid and prevents the brain from being overloaded with situations to decide responses too.
• Once the stimulus is detected by the receptor, an impulse is passed along the sensory neurone to a relay neurone. The relay neurone passes the impulse onto a motor neurone which is connected to an eftector. For example, if the stimulus is a hot object the effector would be the muscles in your hand and arm and the response would be that they contract to move your hand away from the dangerous hot object.
• E.g. knee-jerk reaction and blinking
‘fight or flight’ response
• When mammals are exposed to a potential threat to their survival, a series of automatic responses are triggered to prepare the organism to either fight to survive or to run away from the danger.
• The autonomic nervous system detects the potential threat, sending an impulse to the hypothalamus.
• This results in more impulses being transmitted along the sympathetic nervous system the adrenal-cortical system.
• The effectors are the adrenal glands, which will release more adrenaline and noradrenaline. The release of these hormones triggers the
hypothalamus to stimulate the release of adrenocorticotropic hormone
(ÁCTH) from the pituitary gland.
control of heart rate
The medulla oblongata in the brain controls the heart rate, via the autonomic nervous system
There are two parts:
1) a centre linked to the sinoatrial node to increases heart rate via the sympathetic nervous system
2) Another that decreases heart rate via the parasympathetic nervous system
homeostatic control of heart rate
The heart rate changes in response to pH and blood pressure, and these stimuli are detected by chemoreceptors and pressure receptors in the aorta and carotid artery.
Response to pH:
The pH of the blood will decrease during times of high respiratory rate, due to the production of carbon dioxide or lactic acid. Excess acid must be removed from the blood rapidly to prevent enzymes denaturing.
This is achieved by increasing the heart rate (more impulses via sympathetic nervous system to SAN), so carbon dioxide can diffuse out into the alveoli more rapidly.
Response to pressure:
If the blood pressure is too high this can cause damage to the walls of the arteries and it is important to put mechanisms in place to reduce the blood pressure. This results in more impulses via parasympathetic nervous system to decrease the heart rate.
If the blood pressure is too low, there may be insufficient supply of oxygenated blood to respiring cells and removal of waste. This results in more impulses via sympathetic nervous system to increase the heart rate.
Muscles
There are three types of muscle fibres:
• Skeletal muscles: Most muscle is skeletal, and this is attached to the skeleton and responsible for causing movement of the skeleton.
• Cardiac muscles: The heart contains cardiac muscle. It is myogenic, meaning it does not require input from the nervous system to contract and relax.
• Involuntary (smooth) muscles: This is the muscle that lines organs and blood vessels. By contracting and relaxing, it causes movement of the contents of an organ or blood vessel.
Neuromuscular junction
This is a synapse that occurs between a motor neurone and a muscle and is very similar to a synaptic junction.
neuromuscular junction vs cholinergic synapse
neuromuscular junction-Unidirectional due to the neurotransmitter receptors only being on the post synaptic membrane
-Only excitatory
-Connects motor neurone to muscles
-End point for the action potential
-Acetylcholine binds to receptors on muscle fibre membranes
cholinergic synapse-unidirectional due to the neurotransmitter receptors only being on the post synaptic membrane
-could be excitatory or inhibitory
-connect two neurones, which could be sensory, relay or motor
-a new action potential is generated in the next neurone
-acetylcholine binds to receptors on post-synaptic membrane of neurone
muscles
-Muscles act in antagonistic pairs against an incompressible skeleton to create movement. This can be automatic as part of a reflex response or controlled by conscious thought.
-Myofibrils are made up of fused cells that share nuclei and cytoplasm, known as sarcoplasm, and there is a high number of mitochondria.
sarcomere
Muscle fibres are made up of millions of myofibrils which collectively bring about the force to cause movement.
Myofibrils are made up of two key types of protein, myosin and actin, that form a sarcomere.
contraction
A band-length of myosin
H zone- where you have just myosin no actin
I band- where you have just actin with no myosin.
Z line-barrier or end of one of the sarcomeres
-when muscles contract, you slide actin fibres closer together, A band constant, because myosin simply slides actin closer together, H zone decreases in size, I band decreases, Z lines are closer together
Sliding filament theory
- When an action potential reaches a muscle, it stimulates a response.
- Calcium ions enter & cause the protein tropomyosin to move & uncover the binding sites on actin.
- Whilst ADP is attached to the myosin head, the myosin heads bind to the actin to form a cross-bridge.
- The angle created in this cross-bridge creates tension and as a result the actin filament is pulled and slides along the myosin. In doing so the ADP molecules is released.
- An ATP molecule then binds to the myosin head & causes it to change shape slightly. As a result it detaches from the actin.
- Within the sarcoplasm there is the enzyme ATPase, which is activated by the calcium ions, to hydrolyse the ATP on the myosin head into ADP & releases enough energy for the myosin head to return to its original position.
- This entire process repeats continually whilst the calcium ions remain high, & therefore whilst the muscle remains stimulated by the nervous system.
ATP and phosphocreatine
Active muscles need a high concentration of ATP
The chemical phosphocreatine, which is stored in muscles, assists this by providing phosphate to regenerate ATP from ADP.
