REFLEX ARCS AND REFLEX ACTIONS JANUARY 7 2011

REFLEX ARCS AND REFLEX ACTIONS JANUARY 7, 2011 CSEC HSB POOL 5: 4 MRS. HAUGHTON

PLANT AND ANIMAL RESPONSES

IMPORTANCE OF ORGANISMS RESPONSES TO STIMULI 1. For the survival of the organism. 2. So animals avoid unsuitable conditions. 3. Shoots grow to light to make food, roots grow towards gravity to get water. 4. Hunted animals avoid predators. 5. Male and female are able to detect and respond to the opposite sex. 6. Some plant leaves close when touched to prevent damage. 7. Man maintains a constant body temperature as a response to changes in temperature (homeostasis).

NERVE CELLS • A nerve cell carries nerve impulses quickly from receptors to effectors. • Nerves are the longest cells in the body. • Once damaged, they cannot be regenerated.

NERVE CELLS • There are three types of nerve cells: 1. Sensory nerve cells: receive stimuli from receptors 2. Relay nerve cell: pass impulse from sensory to motor nerve cell. 3. Motor nerve cell: sends impulse to effectors

SENSORY NERVE CELL

MOTOR NERVE CELL

RELAY OR INTERMEDIATE NERVE CELL

HOW NERVE CELLS FORM A REFLEX ARC

Complete the following table of differences on the three types of nerve cells Sensory nerve cell Motor nerve cell Relay nerve cell Is very long. Has a cell body. Impulses travel away from the cell body Carries impulses from receptor to brain or spinal cord. Has myelin sheath and nodes of Ranvier.

SYNAPSE

DEFINITIONS

• STIMULUS: a change in the external or internal environment. • RESPONSE: a change in the activity of an organism or part of an organism as a result of a stimulus.

• RECEPTOR: part of an organism which detects the stimulus e. g. sense organs in animals.

• EFFECTOR: part of an organism which responds to the stimulus e. g. muscles and glands in animals.

• CONDUCTOR: part of the organism which links the receptor to the effector e. g. the nerves in animals.

IMPORTANCE OF RESPONSE TO STIMULI

• For survival. • To avoid unsuitable conditions. • So prey avoid predators. • Males and females are able to detect and respond to the opposite sex.

• Man responds to changes in temperature and body temperature remains constant. • The pancreas secretes insulin as a response to high blood glucose levels.

CLASSWORK

Draw the following table. STIMULUS RESPONSE RECEPTOR EFFECTOR

• Use the words below to complete the table. • • • LIGHT BICEPS BLINKING TASTEBUDS PUPIL OF EYE ODOUR RED SKIN KICK • RETINA SALIVARY GLANDS • INCREASED HEART RATE • FIVE HUNDRED DOLLAR BILL

NERVOUS SYSTEMS IN ANIMALS

THE PARTS OF THE BRAIN

THE AUTONOMIC NERVOUS SYSTEM • This is a branch of the peripheral nervous system which controls the involuntary actions of the body. • It is divided into two antagonistic nerve systems which are the parasympathetic (mostly stimulates) and sympahtetic (mostly inhibits).

BODY PART PARASYMPATHETIC IC Pupil Contract Dilates Tear glands Inhibit Uninhibits Salivation Increase Decrease Heart Slows Accelerates Bronchi Constricts Dilates Digestive function Increases Decreases of stomach Adrenal glands Secrete adrenaline Digestive function of intestines Bladder Increases Decrease Contract Inhibit bladder contraction

REFLEX ACTIONS

• A reflex action is a muscle or gland’s rapid response to a stimulus and does not require conscious thought or control. • E. g. a knee jerk, coughing, sneezing, blinking, withdrawal from danger, or pupil reflexes. • Reflex actions are important for survival.

REFLEX ARCS

• The pathway of nerves between receptor and effector is called a REFLEX ARC. • These events are unlearned and bring together the receptors, CNS, PNS and effectors. • The steps in a reflex arc are as follows:

HOW NERVE CELLS FORM A REFLEX ARC

1. A STIMULUS is applied. 2. The RECEPTOR is stimulated. 3. Nerve impulses travel along the SENSORY NEURONE into the spinal cord (dorsal root). 4. Impulses travel to the RELAY NEURONE. 5. The impulse then travels along the MOTOR NEURONE which leaves the spinal cord (ventral root). 6. The motor neurone carries the nerve impulse to the effector which is stimulated to work.

SIMPLE REFLEX ARC

CRANIAL VS. SPINAL REFLEXES • In cranial reflexes, impulses pass through the brain. • In the spinal reflex, impulses pass through the spinal cord. • E. g. the pupil reflex. If a bright light is shone in the eye, the nerve impulse travels along the nerves traveling through the brain instead of through the spinal cord. • E. g. the knee jerk reflex, or touching a hot plate. The impulses travel through the spinal cord instead of through the brain.

CONDITIONED REFLEXES

• These reflexes occur when the pattern of simple reflex is changed by a period of conditioning or learning. • An example is Pavlov’s dogs. A dog produces saliva when it smells food (simple reflex), but not when a bell is rung.

• If the bell is rung each time the dog is given food, after a few days, the dog will salivate at the sound of the bell even if there is no food present. • The dog has become conditioned to associate the sound of the bell with food.

CLASSWORK • Describe two conditions that have occurred to you or which you have observed that are conditioned reflexes.

SENSES AND SENSE ORGANS • Sense organs are used by animals to detect the stimuli around them. They therefore contain cells called receptors. • The nose and mouth detect chemical stimuli so contain chemoreceptors.

• The skin and ears detect mechanical stimuli so contain mechanoreceptors. • The eyes detect light stimuli so contain photoreceptors.

THE NOSE

THE NOSE

THE NOSE and TONGUE • Scents from objects and the flavour from foods must first dissolve in the moist lining of the nose or the tongue before detection by these organs.

THE EAR

HEARING • When hearing, sound waves are trapped by the pinna and are directed to the inner ear where it causes the 3 small bones to vibrates against one another and the eardrum. • It then causes the cochlea (in the inner ear) to vibrate. • The auditory nerve then picks up the stimulus and directs it to the brain to be heard.

BALANCE • The three semi-circular canals found in the inner ear at 90 degrees to one another are responsible for the detection of position and movement of the head relative to gravity. • They are therefore necessary for balance and co -ordination as changes in the position of the head causes the fluid in the canals to move.

THE SKIN

BODY TEMPERATURE AND SKIN

THE SKIN AND TEMPERATURE REGULATION