Nervous System - Reflexes

Receptors

Detect changes in external or internal environment, different types to detect different stimuli

Types of receptors

Thermoreceptors, osmoreceptors, chemoreceptors, touch receptors

pain receptors

Thermoreceptors

Detect temperature, located in skin and hypothalamus

Osmoreceptors

Detect changes in osmotic pressure and can stimulate hypothalamus, which controls water balance, located in hypothalamus

Chemoreceptors

Pick up on changes in certain chemicals, located in nose, tongue and blood vessels

Touch receptors

Detect different depths of touch and some detect vibrations of pressure. Located on skin surface for light touch, deeper for vibrations and pressure

Pain receptors

Detect tissue damage, concentrated in skin and mucous membranes, don't adapt to pain

Reflex

A rapid, automatic response to change in the external/internal environment

Properties of all reflexes

Stimulus is required (not spontaneous)

Involuntary (occurs without any conscious thought)

Automatic response (does not require the brain)

Rapid (very few interneurons/synapses involved)

Stereotyped (occurs in the same way every time)

Spinal reflex

Relfex carried out by spinal cord alone

Reflex arc

Pathway or nerve impulse follows, travelling from receptor to effector

Spinal reflex arc

Nerve impulse from receptor to effector via spinal cord

Components of a reflex arc

1. A receptor reacts to a change in the internal or external environment by initiating a nerve impulse in a sensory neuron

2. A sensory neuron carries a nerve impulse towards the spinal cord

3. There is at least one synapse between neurons, so impulse can be directly passed to motor neuron or go through an interneuron

4. Motor neuron carries the nerve impulse to an effector

5. An effector receives the nerve impulse and carries out response

6. Message is sent to brain so we are aware of what's happened

Categories of reflexes

Protective reflexes - present from birth

Innate reflexes - automatic instinctive unlearned reaction to stimulus (genetic), e.g suckling, chewing, following movements with eyes

Acquired reflexes - complex motor patterns that are learned through constant repetition, e.g catching a ball, braking a car

Similarities between nervous and endocrine system

Some substances function as both neurotransmitters and hormones (e.g noradrenaline, ADH)

Some hormones are secreted by neurons into extracellular fluid

Some hormones and neurotransmitters have same effect on target cells

Differences between nervous and endocrine system

Nature of message:

Nervous - electrical pulses and neurotransmitters

Endocrine - hormones

Transport of message:

Nervous - neuron axons

Endocrine - bloodstream

Cells affected:

Nervous: Muscle and gland cells

Endocrine: All body cells

Type of response:

Nervous: Usually local + specific

Endocrine: May be general + widespread

Time taken to respond:

Nervous: rapid

Hormones: can be seconds - days

Duration of response:

Nervous: short

Endocrine: longer lasting

Effectors:

Nervous - just one effector

Endocrine - can affect multiple organs