animal responses

• Nervous system

  Made up of the peripheral nervous system (PNS) and the central nervous system (CNS)
• Peripheral nervous system (PNS)

  • Includes the receptors, sensory and motor neurones
• Central nervous system (CNS)

  • Includes the coordination centres, such as the brain and spinal cord
• Nervous system categorisation

  • Autonomic nervous system
  • Somatic nervous system
• Autonomic nervous system

  Works constantly, subconsciously (e.g. digestion)
• Somatic nervous system

  Consciously controlled, voluntary (e.g. choosing to stand up)
• Human brain

  • Coordinates responses
  • Made up of billions of neurones
• Key structures of the brain

  • Cerebrum
  • Cerebellum
  • Medulla oblongata
  • Hypothalamus
  • Pituitary gland
• Cerebrum

  • Largest part of the brain
  • Outer layer is the cerebral cortex
  • Made up of two hemispheres
  • Controls conscious thoughts, language, intelligence, personality, high-level functions and memory
• Cerebellum

  • Looks like a mini cauliflower
  • Responsible for coordinating movement, muscles and balance
• Medulla oblongata

  • Above the spinal cord
  • Centre of control for unconscious activities such as breathing and heart rate
• Hypothalamus

  Small part of the brain responsible for homeostasis, such as temperature and water balance
• Pituitary Gland

  Small lobed structure known as the master gland because it secretes many hormones to coordinate several responses such as the oestrous cycle and osmoregulation
• Reflex

  Rapid, involuntary response to danger that by-passes the conscious part of the brain
• Reflex arc

  1. Stimulus detected by receptor

  2. Impulse passed along sensory neurone

  3. Impulse passed to relay neurone

  4. Impulse passed to motor neurone

  5. Effector responds
• Reflex

  • Rapid because it only involves three neurones and therefore has few synapses
  • No conscious decision is involved
• Synapses

  Slow down responses as electrical energy is converted to chemicals that diffuse across the synapse
• '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
• Autonomic nervous system response to potential threat

  1. Autonomic nervous system detects the potential threat

  2. Sends an impulse to the hypothalamus

  3. Results in more impulses being transmitted along the sympathetic nervous system and the adrenal-cortical system

  4. Effectors are the adrenal glands, which will release more adrenaline and noradrenaline

  5. Release of these hormones triggers the hypothalamus to stimulate the release of adrenocorticotropic hormone (ACTH) from the pituitary gland
• If blood glucose is too low

  The adrenal glands will also secrete adrenaline
• How adrenaline increases blood glucose

  1. Adrenaline attaches to receptors on the surfaces of target cells

  2. This causes a protein (G protein) to be activated and to convert ATP into cAMP

  3. cAMP activates an enzyme that can hydrolyse glycogen into glucose
• Medulla oblongata

  Part of the brain that controls the heart rate, via the autonomic nervous system
• Heart rate control

  1. Centre linked to sinoatrial node that increases heart rate via sympathetic nervous system

  2. Centre that decreases heart rate via parasympathetic nervous system
• Factors that change heart rate

  • pH
  • Blood pressure
• Chemoreceptors

  Receptors that detect pH changes
• Baroreceptors

  Pressure receptors in the aorta and carotid artery that detect blood pressure changes
• High blood pressure

  Can cause damage to artery walls
• Low blood pressure

  Insufficient supply of oxygenated blood to respiring cells and removal of waste
• High respiratory rate

  Decreases blood pH due to carbon dioxide or lactic acid production
• Excess acid in blood

  Can cause enzymes to denature
• Increased heart rate

  Allows more carbon dioxide to diffuse out into alveoli to be removed
• Response sequence for high blood pressure

  1. Stimulus - Increased pressure

  2. Receptor - Pressure receptors in aorta and carotid artery stretched

  3. Coordination - More electrical impulses to medulla oblongata, then impulses via parasympathetic nervous system to SAN to decrease electrical impulse frequency

  4. Effector - Cardiac muscle - SAN tissues

  5. Response - Reduced heart rate
• Response sequence for low pH

  1. Stimulus - Decreased pH

  2. Receptor – Chemoreceptor in the wall of the aorta and carotid artery

  3. Coordination - More electrical impulses are sent to the medulla oblongata and then impulses are sent via the sympathetic nervous system to SAN to increase the frequency of electrical impulses

  4. Effector - Cardiac muscle – SAN tissues

  5. Response – Increased heart rate to deliver blood to the heart more rapidly to remove carbon dioxide
• Types of muscle fibres

  • Skeletal muscles
  • Cardiac muscles
  • Involuntary (smooth) muscles
• 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 is a synapse that occurs between a motor neurone and a muscle and is very similar to a synaptic junction. When an impulse arrives at the end of a motor neurone, a neurotransmitter passes across the neuromuscular junction to the effecter to trigger the response.
• Antagonistic pairs

  • Muscles work in antagonistic pairs against an incompressible skeleton to create movement
  • Movement can be automatic as part of a reflex response or controlled by conscious thought
• Myofibril

  Fused cells that share nuclei and cytoplasm (sarcoplasm) and have a high number of mitochondria