Animal Responses

• Division of the nervous system

  
• Central nervous system (CNS)


  Consists of the brain and spinal cord.

  Much of the brain is composed of relay neurones, which have multiple connections enabling complex neural pathways. Most of the cells are non-myelinated (the tissue is grey in colour - also known as grey matter

  The spinal cord contains lots of myelinated neurones making up an outer region of white matter. These myelinated neurones carry an action potential up and down the spinal cord for rapid communication over longer distances

  
• Peripheral nervous system (PNS)


  The role of the PNS is to ensure rapid communication between the sensory receptors, the CNS and effectors

  
• Ganglion


  A small swelling of nerve cell bodies in the peripheral nervous system
• Autonomic nervous system


  Involuntary control of homeostatic mechanisms. It runs to and from the internal organs regulating respiration, heart rate, digestion etc
• Somatic nervous system


  Controls the body's skeletal muscles (voluntary muscle movement)

  
• Sympathetic nervous system


  Operates when body's activities increase (use energy). It also prepares the body for action (increases blood pressure, heart rate, ventilation rate and increases digestion)
• Parasympathetic nervous system


  Operates when the body's activities decrease (restoring energy - e.g. sleeping). This returns the body to normal (decreases blood pressure, heart rate, ventilation rate and inhibits digestion)
• In the sympathetic nervous system, post-ganglionic neurones secrete noradrenaline at the synapse between the neurone and effector, whereas at the parasympathetic nervous system...


  post-ganglionic neurones secrete acetylcholine as the neurotransmitter at the synapse between the neurone and effector.
• The sympathetic and parasympathetic divisions are...


  antagonistic
• Structure of the human brain

  
• Cerebrum


  The largest part of the brain. The cerebrum organises most of our higher thought processes, such as conscious thought and memory. It also controls voluntary actions such as learning and personality

  
• Cerebellum


  Coordinates movement and balance

  
• Hypothalamus


  Responsible for homeostatic responses and controls various physiological processes (such as temperature and water balance)

  
• Pituitary gland


  A small lobed structure that secretes many hormones to coordinate several responses

  
• Medulla oblongata


  Coordinates many of the autonomic (involuntary) responses (such as heart rate and breathing rate)

  
• What is a reflex?


  A rapid autonomic response to a stimulus that is performed without conscious thought.

  
• What is a reflex action?


  Responses to changes in the environment that do not involve any processing in the brain to coordinate the movement.

  A reflex always has a survival value. It may be used to get out of danger, to avoid damage to the body or may be used to maintain balance

  
• What 3 neurones are involved in the reflex arc?


  Sensory neurone

  Relay neurone

  Motor neurone
• Reflex arc


  Once a stimulus is detected by the sensory 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 effector
• What are examples of reflex actions?


  Blinking reflex

  Knee jerk reflex
• What type of reflex is the knee jerk reflex?


  Spinal reflex - The nervous pathway passes through the spinal cord (rather than the brain)
• Knee jerk reflex


  A reflex action that straightens the leg when the tendon below the patella is tapped. It involves coordinated movement and balance. The muscle at the front of the thigh contracts to straighten the leg.

  When the muscles at the front of the thigh are stretched, specialised stretch receptors (muscle spindles) detect the increase in length of the muscle.

  
• The knee jerk reflex consists of...


  2 neurones (sensory ne2 neurones (sensory neurones --> motor neurones). One less synapse involved means the response is quickerurones --> motor neurones). One less synapse involved means the response is quicker
• What are muscles categorised into?


  Skeletal muscle

  Smooth muscle

  Cardiac muscle
• What is the importance of reflex arcs?


  -> Involuntary - They allow the brain to concentrate on complex processes.

  -> Rapid - They ensure a swift response.

  -> Protective - They safeguard the body from potential injuries.

  -> Innate - They are intrinsic mechanisms present from birth, eliminating the need for learning.
• As there is no relay neurone...


  the brain cannot inhibit the reflex. Inhibition relies on rapid myelinated neurones carrying the inhibitory action potentials to the synapse before the motor neurone is stimulated. So in the absence of the relay neurone, the motor neurone is stimulated directly by the the sensory neurone and there is insufficient delay to enable inhibition

  
• While we a walking/running...

  the knee must bend and will stimulate muscle spindles. As action potentials are sent to the muscles, stimulating it to contract, inhibitory action potentials are sent to the synapse in the reflex arc to prevent the reflex contraction of the opposing muscle.
• What is the mechanism of the fight-or-flight response?


  1) The autonomic nervous system detects a threat, and the signal is passed on to the hypothalamus.

  2) The hypothalamus activates the sympathetic nervous system, sending nerve signals to glands and muscles.

  3) The sympathetic nervous system triggers the secretion of adrenaline and noradrenaline from the adrenal medulla, causing various physiological changes (increases heart rate/dilated pupils)

  4) The hypothalamus also communicates with the adrenal-cortical system, stimulating the pituitary gland to release ACTH

  ACTH travels via the bloodstream to the adrenal cortex, stimulating it to release several other hormones to help the body deal with the threat.

  
• What are the physiological changes occur in the fight or flight response?

  
• What is the second messenger model?


  The second messenger model of hormone action involves a hormone (the first messenger) triggering the formation of a second messenger (cAMP) inside the cell, which activates enzymes to carry out a function.

  
• What is an example of the second messenger model?


  The action of adrenaline in the fight or flight response
• Cell signalling pathway for adrenaline


  1) Adrenaline binds to complementary receptor on the cell-surface membrane of a liver cell.

  2) The binding of adrenaline causes the protein to change shape.

  3) This activates the enzyme adenylyl cyclase and the activated adenyl cyclase converts ATP into cAMP.

  4) cAMP acts as a second messenger, binding to and activating many protein kinases via phosphorylation, amplifying the signal from adrenaline.

  5) Protein kinases activate enzymes that catalyse the breakdown of glycogen into glucose.

  6) Glucose moves out of liver cells by facilitated diffusion and into the blood through channel proteins.

  7) This increases the blood glucose concentration so that more glucose can be delivered to body cells for respiration.
• Why is this known as the cascade effect?


  One hormone molecule can generate multiple cAMP molecules. This effect amplifies at each stage, increasing the number of molecules involved.
• Cardiac muscle is...


  myogenic - it can initiate its own own beat at regular intervals
• Why is a coordination mechanism for heart rate needed?


  The atrial muscle has a higher myogenic rate than the ventricular muscle. The two pairs of chambers must contract in a coordinated fashion or heart action will be ineffective
• What controls heart rate?


  The medulla oblongata via the autonomic nervous system

  
• What is the cardiovascular centre?


  The cardiovascular centre in the medulla oblongata of the brain connects with the SAN via accelerator and vagus nerves. These nerves affect the frequency of contractions
• What do the two parts of the cardiovascular centre do?


  -> One centre increases heart rate by sending impulses through the sympathetic nervous system. These impulses are transmitted by the accelerator nerve

  -> One centre decreases heart rate by sending impulses through the parasympathetic nervous system. The impulses are transmitted by the vagus nerve
• What do the accelerator and vagus nerves do?


  -> Action potentials sent down the accelerans nerve causes the release of the neurotransmitter acetylcholine at the SAN and this increases heart rate

  -> Action potentials sent down the vagus nerve release the neurotransmitter acetylcholine, which reduces heart rate