It receives information from receptors and then transmits and interprets the information
It then formulates appropriate responses to be sent to the effector organs
It also controls and coordinates functions throughout the body and helps maintain homeostasis
THE HUMAN NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM (CNS) PERIPHERAL NERVOUS SYSTEM (PNS) ORGANISATION OF THE NERVOUS SYSTEM
ORGANISATION OF THE NERVOUS SYSTEM Links receptors & effectors to CNS : relays signals between CNS & rest of body HUMAN NERVOUS SYSTEM CENTRAL NERVOUS SYSTEM [CNS] PERIPHERAL NERVOUS SYSTEM [PNS] BRAIN SPINAL CORD CRANIAL NERVES [12 pairs] SPINAL NERVES [31 pairs]
AN OVERVIEW OF THE FUNCTIONS OF THE NERVOUS SYSTEM Sensory receptors detect stimuli from int. & ext. environments & initiate nerve impulses carrying information to CNS CNS processes & integrates information by analysing & storing some of it, & then make decisions to initiate suitable responses Motor commands from CNS transmitted to effectors [muscles or glands] to carry out responses 1 3 2
THE HUMAN BRAIN HUMAN BRAIN HYPOTHALAMUS THALAMUS MEDULLA OBLONGATA CEREBELLUM CEREBRUM
THE HUMAN BRAIN SKULL MEDULLA OBLONGATA CEREBELLUM CEREBRUM VERTEBRA SPINAL CORD PITUITARY GLAND THALAMUS HYPOTHALAMUS
The spinal cord is contained within the vertebral column
The spinal cord is surrounded by cerebrospinal fluid which acts as a shock absorber and provides the spinal cord with nutrients.
It consists of white matter and grey matter.
(a) In cross section, the grey matter looks like a butterfly or the letter H.
(b) The grey matter consists mainly of cell bodies of neurones.
(c) The grey matter is surrounded by the white matter .
(d) The white matter comprises myelin-coated axons of neurones that extend the whole length of the spinal cord.
THE SPINAL CORD AND ITS MAIN FUNCTIONS
The spinal nerves emerge from the spinal cord through two short branches or roots. (a) The dorsal root contains the axons of the afferent neurones which conduct nerve impulses from the sensory receptors to the spinal cord. (b) The cell bodies of the afferent neurones are clustered in the dorsal root ganglion (c) The ventral root contains the axons of the efferent neurones which conduct nerve impulses away from the spinal cord to the effectors. (d) The dorsal and ventral roots join to form a spinal nerve. FUNCTION : The spinal cord (a) processes certain types of sensory information and sends out responses via the efferent neurones. (b) contains neurones that convey signals to and from the brain, (c) contains the neural pathway for reflexes
Dendrites are fibres that receive information or signals from other neurones or from the external environment and conduct them towards the cell body.
Dendrites of afferent neurones have special membrane adaptations that allow them to produce signals in response to specific stimuli from the external environment such as pressure, light or heat.
A long, thin fibre called the axon extends outward from the cell body.
• The axon conducts the nerve impulses away from the cell body.
• The axons are usually bundled together into nerves
Nerve impulses are conducted along the axon and finally reach the synaptic terminals [swellings at the branched ends of the axons] located at the far end of each axon.
• The synaptic terminals then transmit these signals to the muscle cells, gland cells or the dendrites of another neurone.
The electrical signals or nerve impulses then travel along the dendrites and converge on the cell body of the neurone.
• The cell body has a nucleus and other organelles which are found in cells.
• The cell body integrates the signals and coordinates the metabolic activities.
Some axons are insulated by a thick coat of material called a myelin sheath .
This sheath protects and insulates the axons, and helps to speed up the transmission of the nerve impulses.
dendrite Cell body Myelin sheath Muscle fibre (effector) Synaptic terminals axon Direction of nerve impulse nucleus 1 4 3 2 5
THE TRANSMISSION OF INFORMATION ALONG THE NEURONE
The transmission of information along the neurone is through electrical signals known as nerve impulses .
An impulse is a wave of positive charges that travel along the axon to the synaptic terminal.
A neurone will not transmit an impulse unless the stimulation is strong enough.
Once the magnitude or size of the stimulation reaches a threshold level, a full-sized impulse is generated to travel the entire length of the axon.
The transmission pathway of information Reception of stimuli by receptors Response by the effectors From the CNS to the effectors Integration & interpretation by the central nervous system From receptors to the central nervous system 1 5 4 3 2
Afferent neurone Efferent neurone Interneurone 1 5 4 3 2 6 Receptors in the ear Muscles in the arm Receptors in the ear pick up the ringing of the doorbell. The nerve impulses pass from the afferent neurones to the interneurones in the brain The receptors trigger nerve impulses in the afferent neurones. From the interneurones, nerve impulses are transmitted to the efferent neurones and then to the muscles The brain interprets the nerve impulses from many interneurones that the doorbell is ringing. The brain also decides that the door should be opened The muscles in the arm carry out the response and open the door 1 2 3 4 5 6 The transmission pathway of information
The transmission of nerve impulses along the three types of neurones Synaptic terminal dendrites axon dendrite Cell body receptor in skin axon myelin sheath Synaptic terminal on muscle fibre Cell body Cell body axon myelin sheath Efferent neurone synaptic terminal Afferent neurone Interneurone
DIFFERENCE BETWEEN STRUCTURE OF AFFERENT NEURONE & EFFERENT NEURONE AFFERENT NEURONE EFFERENT NEURONE Long dendrite, short axon Short dendrite, long axon Cell body at the side of the neurone [not at the end] Cell body at the end of the neurone Begins with receptor Ends with effector