Chapter 13: Coordination and response

Two main systems to control the body

Nervous system: controlled via electrical impulses to bring fast, short lived responses

Endocrine system: controlled via hormones to bring slow, long term responses

Definition of stimulus, receptor and effector

Stimulus: change in the internal or external environment that we can detect

Receptor: detects the stimulus and creates electrical impulses to send around the body

Effector: muscle or gland that brings a response to the stimulus

Central nervous system

Contains brain and the spinal cord

(Peripheral nervous system is on the side)

3 types of neurones

• sensory (receptor → CNS)

• Relay (sensory neurons → motor neurons)

• Motor (CNS → effector)

Adaptations of neurones

1. They can carry electrical impulses

2. Long axons (sensory and motor) because they need to transmit nerve impulses to distant parts of the body

3. Relay neurons are found in the brain and link between sensory and motor neurons in the spinal cord

Reflex action

Rapid, automatic responses of the nervous system that does not involve the brain.

Happens without conscious thought.

Important because it reduces harm and coordinates everyday daily functions

Reflex arc

• receptor detects stimuli

• Receptor electrical impulses Endocrine system to sensory neuron along the length of spinal cord

• Impulse is carried by neurotransmitters through the synapse to attach to the receptors of dendrites of relay neurons by diffusion.

• Same thing for relay → motor neuron

• Electrical impulse goes to effector

• Effector carries out a response

• Later relay neurones sends impulse to the brain (after reflex action is done)

Synapse

Junction between two neurons. Allows impulse to travel from one axon terminal to dendrite of another neuron

Diffusion across synapse

1. Electrical impulse travels along an axon

2. Triggers vesicles to release neurotransmitters (they allow transmission of information across synaptic gap)

3. Neurotransmitters diffuse across the synapse and bind with receptor molecules of dendrites

4. Nerve impulses is trigger

The eye (Sense organ)

• cornea: refracts light, focusing it on the retina

• Lens: refracts light, focusing it on the retina

• Fovea: part of retina that provides clearest vision

• Retina: contains light receptor cells

• Optic nerve: bundle of neurons that carries electrical impulses from retina to brain

• Blind spot: part of retina where optic nerve enters the eye (doesn’t contain receptor cells)

Pupil reflex

Dim light

• pupils dilate: to allow as much light as possible

• Circular muscles relax

• Radial muscles contract

Bright light

• pupils constrict: to prevent eye damage/protect the retina

• Circular muscles contract

• Radial muscles relax

Light receptor cells

Rods

• not colored vision

• Allows vision in dim light as it is more sensitive to light than cones

• Rods are on the side (away from the fovea)

• No rods in the fovea

Cones

• for colored vision (R, B, G)

• Most cones in fovea

• Uneven distribution of cones in retina

Accommodation

Changes that happen in an eye to allow objects to be seen at different distances

Accommodation for distant objects

Light enters in parallel lines

• ciliary muscles relax

• Suspensory ligaments stretch

• Lens get thinner

Light is refracted less strongly

Insulin

Made in: pancreas

Organs it affects: liver and muscles

Effect: lowers blood glucose concentration by converting glucose → glycogen

Testosterone

Where it’s made: testis

Organ it affects: reproductive system organs

Effect: puberty in males

Oestrogen

Where it’s made: ovaries

Organ it affects: reproductive system organs

Effect: puberty in females and controlling menstrual cycle

Adrenaline

Where it’s made: adrenal gland

Organ it affects: eyes, lungs, brain, liver, muscles

Effect: getting ready for flight or fight response

Adrenaline affect on organs

Eyes: pupils dilate to allow more light to retina

• this is for better vision to run/fight better

Heart: rate increases to increase delivery of glucose and oxygen to muscles around the body

• increases rate of aerobic respiration for muscles, releasing more energy to move

Lungs: breathing rate increases to increase supply of oxygen into the blood and remove CO2 quickly

• increases rate of aerobic respiration for muscles, releasing more energy to move

Liver: increases levels of blood glucose concentration from breakdown of glycogen stored in liver and muscles

• more glucose for more aerobic respiration

• Increases metabolism

Homeostasis

Homeostasis: Maintaining a constant internal environment (controlled by a mechanism called negative feedback)

Controls:

• body temperature

• Blood glucose concentration

Negative feedback

When a deviation from the norm is detected, it will initiate a response to return the system to its norm

Thermoregulation

Maintaining constant internal temperature

Measured by

• receptors in the brain (hypothalamus)

• Receptors in the skin

Cooling mechanisms

Sweating

• evaporation of sweat on skin surface takes heat up and away

Vasodilation (arteries dilating)

• blood vessels to skin capillaries get wider so more heat is lost

• This is because more blood is carried to the surface of the skin

• Heat loss by radiation

Heating mechanisms

Shivering

• muscles contracting need energy and some is released as heat

Hair stands up by hair erector muscle

• erect hairs trap a layer of air around the skin, which acts as an insulator

Vasoconstriction (arteries constricting)

• blood flow in capillaries slow down because arteriales leading to skin capillaries get narrower

• So less blood is carried to surface of the skin

• Less heat loss by radiation

Blood glucose control

Glucose is transported un the blood (dissolved in the plasma)

When blood glucose concentration is too high:

• insulin (a hormone), produced by pancreas stimulates liver cells to convert glucose to glycogen in the liver

• More glucose is taken by cells for respiration

When blood glucose concentration is too low:

• glucagon (a hormone), produced by pancreas stimulates liver cells to convert glycogen to glucose.

Type 1 diabetes

• caused by genetics

• Pancreas isn’t making enough insulin so blood glucose concentration is high

• Insulin injections work

Tropism

A response by a plant to a stimukus

2 types of tropisms

• gravitropism: response in which parts of the plant grow towards/away gravity

• Phototropism: response in which parts of the plant grow towards/away light

Auxin

• plant hormone that diffuses down the shoot tip

• Auxin is unequally distributed in response to light/gravity.

• Auxin stimulates cell elongation allowing shoot to bend towards light stimulus