2.89-2.94

• How is information transmitted by the endocrine system?


  Information is transmitted by the endocrine system when hormones are carried by the blood to target cells.
• Hormones: immediacy of responses 


  Hormones are used to control functions that do not require instant responses; this is because hormonal transmission is slow in comparison to nervous transmission.
• examples of hormone glands?

  Examples of hormone, or endocrine, glands include:

  • Ovaries
  • Testes
  • Pituitary gland
  • Pancreas
  • Adrenal gland
• hormones: affecting cells 


  Hormones only affect specific target cells because they bind to receptors which are only present on the surface of these target cells.
• hormonal responses 


  Hormonal responses can be very long-lived, while the effect of a nerve impulse stops as soon as impulse transmission stops.
• what is a bundle of neurones

  a nerve
• What is the role of the central nervous system?


  The role of the central nervous system is to receive informationfrom the senses and coordinate a response.
• function of sensory neuron 


  Sensory neurones carry impulses from sense organs to the central nervous system (CNS).
• function of motor neurones 


  Motor neurones carry impulses from the CNS to effectors(muscles or glands).
• function of myelin sheath

  The myelin sheath insulates axons in order to increase the speedat which nerve impulses are transmitted.
• flow diagram to show the pathway of an electrical impulse through the nervous system.


  stimulus → receptor → sensory neurone → CNS → motor neurone → effector → response
• Define the term neurotransmitter.


  Neurotransmitters are chemical signalling molecules used to transfer signals between neurones at synapses.
• How is an impulse passed across a synapse?

  An electrical impulse travels across the gap at a synapse as follows:

  • Neurotransmitters are released and diffuse across the gap between neurones
  • Neurotransmitters bind to receptor molecules on the second neurone
  • A new electrical impulse is generated in the second neurone
• What happens to neurotransmitters after impulse transmission at a synapse has finished?


  After impulse transmission has finished the neurotransmitters are broken down by enzymes to prevent continuous stimulation of the second neurone.
• reflex responses


  Reflex responses do not involve conscious processing in the brain; they are automatic and rapid, meaning that the brain may not become consciously aware of the stimulus until after the body has responded.
• Define the term reflex.


  A reflex is an involuntary reaction that does not involve conscious processing in the brain. It is automatic, rapid, and helps minimise damage to the body.
• Write a flow diagram to show the pathway of a reflex arc when withdrawing from a hot object.

  In a reflex arc for withdrawing from a hot object the pathway is as follows: 

  Hot object (stimulus) → sensory neurone → relay neurone in spinal cord → motor neurone → muscle (effector) → contraction to move away from object (response)
• Why are reflex responses important?


  Reflex responses are important because they are quick and automatic, allowing the body to avoid injury.
• Name the light-sensitive receptor cells found in the retina of the eye

  The receptor cells in the retina which are sensitive to light arerods and cones.
• What is the function of the optic nerve?

  The optic nerve is responsible for transmitting electrical impulses from the receptor cells in the retina to the brain.
• role of the fovea in the retina


  The fovea is a region of the retina with the highest density of cones; light focused here results in detailed, colour vision.
• iris: muscles 


  The circular and radial muscles of the iris contract and relax to alter the light that can enter the eye through the pupil.
• role of the cornea in the eye?

  The cornea is a transparent layer located on the surface of the eye. It provides protection and plays a role in focusing light onto the retina.
• Define the term blind spot in relation to the eye.


  The blind spot is the area where the optic nerve exits the retina; it lacks receptor cells, thus creating a spot where no visionoccurs.
• Name the stimulus which is detected by the eye.


  The eye is a highly specialised sense organ which detects light stimuli.
• what is the optic nerve made up of 


  The optic nerve is made up of sensory neurones which transmits electrical impulses from the receptors in the retina to the brain.
• What is the role of the suspensory ligaments in the eye?


  The suspensory ligaments connect the ciliary muscle to the lens, facilitating changes in lens shape during accommodation. This allows the eye to focus on near or distant objects.
• Which receptor cells are affected in those with colour blindness?

  The receptor cells that are affected in colour blindness are the cone cells. These are the receptors which are responsible for detecting light wavelength, so they provide colour vision.
• Define the term accommodation in the context of eye function.


  Accommodation is the process by which the lens of the eye changes its shape to focus on objects at different distances. It is facilitated by the contraction or relaxation of the ciliary muscles and adjustment of the suspensory ligaments.
• Define the term refraction.


  Refraction is the bending of light as it enters a medium of a different density, e.g. the lens of the eye.
• Name the two components of the eye that are responsible for refracting light.

  Two structures of the eye which are responsible for refraction of light are:

  • Cornea
  • Lens
• What is the role of the ciliary muscle in accommodation?

  The ciliary muscle controls the shape of the lens by contracting to thicken it during close vision and relaxing to flatten it during distant vision. This is known as accommodation.
• What happens to the lens and ciliary muscles when focusing on a near object?

  When focusing on a near object:

  • The ciliary muscles contract
  • The suspensory ligaments loosen

  This causes the lens to become thicker (more curved), increasing refraction of light for close vision.
• ciliary muscles and suspension ligaments when focusing on a distant object

  When focusing on a distant object:

  • The ciliary muscles relax
  • The suspensory ligaments tighten

  This pulls on the lens, making it thinner and less curved; this reduces refraction of light for distant vision.
• purpose of the pupil reflex?


  The pupil reflex protects the retina from damage in bright light or improves vision in dim light. It does this by adjusting the size of the pupil to control the light entering the eye.
• Name the antagonistic muscle pair which is responsible for the pupil reflex.

  The antagonistic muscle pair responsible for the pupil reflex is the:

  • Circular muscles
  • Radial muscles

  Both of these muscles are found in the iris of the eye.
• radial and circular muscles responding to dim light 


  Radial muscles contract and the circular muscles relax in response to dim light. This results in dilation of the pupil to allow more light to reach the retina.
• What changes occur in the pupil when exposed to bright light?


  In bright light the circular muscles contract and the radial muscles relax. This causes the pupil to constrict, reducing the light entering the eye and protecting the retina from damage.
• Why is temperature regulation in mammals important?


  Temperature regulation ensures that core temperature stays at around 37 °C. This maintains optimal enzyme activity and therefore efficient physiological function.
• How does sweating increase heat loss from the body?


  Sweating increases heat loss when sweat evaporates from the skin surface. The evaporation of sweat transfers heat energyaway from the skin.