Plant and animal responses

• Why does an organism need a communication system?

  to detect changes in environment

  to enable cell signalling between body parts

  to coordinate a range of effectors to carry out responses to the sensory input

  to carry out suitable responses
• How is the Nervous system organised?

  Into the central nervous system (CNS) and the Peripheral nervous system (PNS)
• How is the CNS organised?

  Into the Spinal cord and the Brain

  > The Brain is composed of relay neurones which have multiple connections enabling complex neural pathways.

  Most of these cells are non-myelinated and known as grey matter.

  > The Spinal cord contains large number of myelinated neurones which carry APs up/down spinal cord for rapid communication over long distances.

  The cord is protected by the vertebral column: between each vertebrae peripheral nerves enter/leave carrying AP to/from rest of the body.
• How is the PNS organised?

  Into the sensory and motor system
• How is the motor system in the PNS broken down further and organised?

  Into the Somatic NS and the autonomic NS.

  The autonomic NS is further broken down into Sympathetic and Para-sympathetic NS.
• What is the role of the CNS?

  Stimulate muscle action

  Control balance and posture

  Regulate temperature
• What is the role of the PNS?

  To ensure rapid communication between sensory receptors, the CNS and effectors.
• (Subset of PNS) How is the Sensory Nervous system structured?

  Fibres entering CNS are dendrons of the sensory neurones.

  Neurones conduct APs from the sensory receptors into the CNS.

  Neurones have cell body in dorsal root, leading into spinal cord, and a short axon connecting to other neurones in the CNS.
• (Subset of PNS) How is the Motor Nervous system structured?

  conducts action potentials from CNS to effectors through somatic and autonomic NS
• (Subset of Motor NS) How is the somatic NS structured?

  > Somatic NS consists of motor neurones conducting APs from CNS to effectors under voluntary control. For example: skeletal muscles.

  > Motor neurones are mostly myelinated so responses are rapid.

  > There is always one motor neurone that connects CNS to the effector.
• (Subset of Motor NS) How is the autonomic NS structured?


  > Autonomic NS consists of motor neurones conducting APs from CNS to effectors not under voluntary control. For example: cardiac muscle, glands, airways.

  > These motor neurones are non-myelinated and do not require rapid responses.

  > There is always two motor neurones, joined at the Ganglia, that connect CNS and effector.

  > At rest APs pas along neurones of parasympathetic and sympathetic systems at a low frequency
• (Subset of autonomic NS) What is the structure of the Parasympathetic NS?

  > Consists of few nerves leading out of CNS to different effectors.

  > Ganglia is in effector tissue and has long pre-ganglionic neurones and short post-ganglionic neurones.

  > It uses acetylcholine as a neurotransmitter.
• (Subset of somatic NS) What is the structure of the Sympathetic NS?


  > Consists of many nerves leading out if CNS to different effectors.

  > Ganglia is outside CNS and has short pre-ganglionic and long post-ganglionic neurones.

  > Noradrenaline is used as a neurotransmitter.
• What are the effects of the Parasympathetic NS?

  > It decreases activity to conserve energy so active in sleep.

  > decreases heart rate and ventilation

  > increases digestive activity
• What are the effects of the Sympathetic NS?

  > It increases activity to prepare body for fight or flight response.

  > Increases heart rate and ventilation.

  > Decreases digestive activity.
• What is the structure and function of the cerebrum?

  Function: organises conscious thought processes - memory, intelligence, emotional responses.

  Structure: Cerebral cortex divided into areas with specific roles...

  Sensory areas - receive AP indirectly from sensory receptors.

  Association areas - compare sensory inputs with previous experiences to judge an appropriate response.

  Motor areas - send APs to effectors.

  Larger areas used for more complex movements in body.
• What is the structure and function of the cerebellum?

  Function: coordinates voluntary muscular contraction and balance including..

  > judging position of objects and limbs in sports

  > tensioning muscles to use tools/ musical instruments

  > coordinating contraction/ relaxation of antagonistic skeletal muscles for walking

  These are strengthened by practice.

  Neurones conduct AP to motor areas.
• What is the function of the Hypothalamus?


  Controls homeostatic mechanisms in body.

  It contains own sensory receptors within structure for..

  > Temperature regulation: detects changes in core body temperature and temperature receptors in skin.

  Initiates negative feedback via hormonal or nervous system.

  > Osmoregulation: Osmoreceptors within hypothalamus monitor water potential in blood.

  When Water potential changes, osmoregulatory centre initiates response via hormonal system.
• What is the structure and function of the Pituitary Gland?


  Gland is in conjunction with the Hypothalamus.

  > (Lobe 1) Posterior Lobe is linked by specialised neurosecretory cells.

  ADH hormones, made in Hypothalamus, pass down neurosecretory cells and are released into blood from pituitary gland.

  > (Lobe 2) The Anterior Lobe produces own hormones that are released into blood in response to releasing factors received by the hypothalamus. These hormones control physiological processes in body: stress, growth, reproduction.
• What is the function of the Medulla Oblongata?

  Coordinates autonomic responses in body:

  > heart rate

  > circulation and blood pressure

  > rate and depth of breathing

  Non skeletal muscles, cardiac and involuntary smooth, contract by sending APs through Autonomic nervous system.
• What is meant by a reflex arc?

  Neural pathway, containing effector and receptor, that controls a reflex action.
• How does the Corneal reflex work?

  1> Sensory neurone from cornea enters the pons in brain which connects the sensory neurone to a relay neurone.

  2> This passes an AP to motor neurone which passes back out brain to facial muscles causing eyes to blink.

  > The pathway in this reflex is direct and short allowing it to be rapid.
• How can the Corneal reflex (Blinking reflex) be recognised by the Cerebrum be overridden by conscious control?

  1> Sensory neurones involved in corneal reflex also passes APS to myelinated neurones in pons, which carry APs to sensory region in Cerebral cortex, informing brain stimulus has occurred.

  2> Cortex can send inhibitory signals to motor centre in pons .

  4> Myelinated neurones carrying impulses to/from cerebral cortex transmit APs more rapidly than non-myelinated relay neurones in pons.

  5> Inhibitory APs can prevent formation of an AP in motor neurone, overriding control over reflex.
• How does the Optical reflex work?

  Stimuli is detected photoreceptors on retina and reflex is controlled by optical centre in cerebral cortex.

  Response is slower than the Corneal reflex.
• How does the Knee jerk reflex work?

  Stretch reflex controlled by Spinal reflex:

  1> Quadricep stretches

  2> Specialised stretch receptors, muscle spindles, detect increase in muscle length

  3> If stretch is unexpected from Cerebellum then reflex action causes contraction of same muscle, causing knee jerk.

  Pathway: Sensory>motor

  Due to lack of relay neurone in pathway, the brain cannot inhibit the very rapid reflex.
• How can the Cerebellum inhibit action when walking/running?

  1> APs sent to hamstring muscles, stimulate it to contract.

  2> Inhibitory APs are then sent to synapse in reflex arc via myelinated neurones rapidly, which prevents reflex contraction of quadricep.
• What are reflex actions?

  Involuntary responses to changes in environment without any processing in brain to control movement.

  They have survival values to:

  > Get out of danger

  > Avoid damage to areas of the body

  > Maintain balance
• What is the coordination of flight or fight response in Mammals?


  Detection of threats in environment stimulate physiological changes in organism to prepare for activity including:

  > Dilated pupils - more light sent to eyes

  > Increased Heart rate and Blood pressure - increases blood flow containing oxygen and glucose to muscles

  > Increased metabolic rate - converts glucose to usable energy like ATP

  > Increased ventilation rate and depth - increases gaseous exchange for more aerobic respiration
• How are flight or fight responses coordinated?

  In the autonomic system - sympathetic and parasympathetic system.

  1> Input feeds into sensory centre in Cerebrum, which passes signals to association centres.

  2> If threat is recognised, Cerebrum stimulates Hypothalamus which increases activity in Sympathetic NS and stimulates release of hormones from Anterior Pituitary gland.
• The sympathetic NS stimulates the Adrenal Medulla, which releases Adrenaline, how does it signal cells to create response in body?


  1> 1st messenger, adrenaline, binds to adrenaline receptors on plasma membrane of target cell.

  2> This activates a G protein on inner surface of membrane, activating Adenyl Cyclase which converts ATP to cAMP, 2nd messenger.

  3> cAMP then activates enzyme action within cell.
• Release of hormones from Anterior Pituitary gland

  > Hypothalamus secretes releasing factors into blood which pass down portal vessel to pituitary gland.

  > This stimulates release of Tropic hormones from Anterior region of gland, which activates endocrine glands:

  > Corticotropin-releasing hormone (CRH) causes release of adrenocorticotropin hormone (ACTH).

  > ACTH passes through blood stimulating adrenal cortex to stimulate Corticosteroid hormones, cortisol, to regulate metabolism through Glycogenolysis and Glyconeogenesis.
• How, and why, is Thyroxine released from the endocrine gland, thyroid, through stimulation from the pituitary gland as a result of a flight/fight response?

  > Thyrotropin-releasing hormone (TRH) causes release of Thyroid-stimulating hormone (TSH)

  > This stimulates thyroid gland to release more thyroxine, increasing metabolic rate and cell sensitivity to adrenaline.
• What is the basic mechanism behind muscular contraction?

  Muscle cells arranged into fibres, which contract to become shorter creating a force.

  Contraction achieved by interaction between actin and myosin in these cells, arranged in antagonistic pairs, so when one contracts, the other elongates.
• What is the structure of (involuntary) smooth muscle?

  > contains bundles of actin and myosin in circular layers

  > contracts slowly and regularly so does not tire quickly

  > found in walls of tubular structures: digestive system and blood vessels

  > controlled by the autonomic NS
• What is the structure of Cardiac muscle?


  > forms muscular part of the heart and appears striped under a microscope.

  > fibres branch to form cross fibres which ensure electrical stimulation spreads evenly over walls of chambers and that contraction is squeezing action rather than one dimensional.

  > cells joined by intercalated discs with specialised fused membranes to produce gap junctions which allow diffusion of ions between cells.

  > APs pass quickly between fibres so they do not tire easily.
• What is the structure of (voluntary) Skeletal muscle?

  > occurs at joints in the skeleton.

  > contraction causes movement of skeleton by bending/straightening joint quickly so tires quickly.

  > each fibre is multinucleate surrounded by sarcolemma (cell membrane).

  > The sarcoplasm (cell cytoplasm) is specialised to contain many mitochondria and sarcoplasmic reticulum.

  > contents are arranged into myofibrils, divided by sarcomeres, which contain Actin and Myosin which form thin and thick filaments forming the light(I) and dark (A)bands.
• The Neuromuscular junction


  Junction between muscle and NS

  Its contractions are stimulated by Somatic NS
• Stimulation of contraction

  1> APs arriving at end of axon open Ca2+ channels in membrane, so ions flood into end of axon.

  2> vesicles of acetylcholine move and fuse with end of membrane.

  3> Ach diffuse across gap and fuse with receptors in the Sarcolemma.

  4> This opens Na+ channels, allowing Na+ to enter muscle fibres, causing depolarisation of the Sarcolemma.

  5> Wave of depolarisation spreads along Sarcolemma and down transverse tubules into muscle fibres.
• Motor unit

  Many motor neurones divide and connect to muscle fibres. When activated they stimulate a contraction.
• Structure of Myofibril

  Consists of contractile units of skeletal muscle containing two protein filaments:

  > thin filaments aligned making light band held by Z line

  > thick filaments making dark band

  These filaments, surrounded by sarcoplasmic reticulum overlap forming the H zone.

  The distance between the two bands is called the sacromere, forming the functionable unit of muscle.

  A) Sarcomere

  B) A band

  C) H zone

  D) Myofibril

  E) Myosin

  F) Actin

  G) Z line