RESPONDING TO THE ENVIRONMENT
HUMANS
HUMAN NERVOUS SYSTEM
Brain
CNS
Cranial nerves Central Nervous System
PNS
Peripheral nervous Spinal cord
system
Spinal nerves
THE FUNCTION OF THE NERVOUS SYSTEM
- 1 Detect changes in the environment and allow the body to react to stimuli
- 2 Enable co-ordination of various activities
3 TYPES OF NEURONS
1 SENSORY NEURON
- Carry impulses from receptors (nerve endings and sense organs) to the central
nervous system (CNS)
- Brain + spinal cord
2 MOTOR NEURON
- Carry impulses from the CNS to the effectors (muscle glands)
- The effectors bring about a response
3 INTERNEURON/CONNECTOR NEURON
- Link sensory neuron to motor neuron
- Carry impulses inside the CNS from a sensory neuron to a motor neuron
IMPULSE DIRECTION
Dendrite Cell body Axon
,DIAGRAMS OF 3 DIFFERENT TYPES OF NEURONS
SENSORY NEURON (Afferent)
Sensory receptor
Dendrite
Myelin sheath (outside membrane)
Cell body
Nucleus
Neurilemma
Axon branches / Axon terminal
MOTOR NEURON (Efferent)
Cell body
Nucleus
Dendrite
Neurilemma
Myelin sheath (outside membrane)
Axon branches
INTERNEURON (Connector)
Dendrite
Cell body
Nucleus
Axon branches
, NERVOUS TISSUE OF THE NEURONS
- The cell body has the following organelles:
- Nucleus
- Cytoplasm
- Mitochondria
- Ribosomes
- Endoplasmic reticulum
Dendrites
- Branching cytoplasmic threads
- Carry impulses towards the cell body
Axon
- Single long outgrowth which conducts impulses away from the cell body
Terminal branches
- Branch endings of the axon
Two membranes cover the axon
- 1 Myelin sheath
- provides electrical insulation
- speeds up the transmission of implants
- 2 Neurilemma
- encloses the myelin sheath
TRANSPORTATION OF NERVE IMPULSES
- More than 1 neuron is involved in the transport of nerve impulses
- Neurons are lined up so that the axon terminals of 1 neuron lay next to the dendrites
of another
- Neurons aren’t directly connected
- There is a microscopic gap (synapse) between the axon terminals of one neuron and
the dendrite of another
- Nerve impulses are carried along the neuron by electrical impulses
- Communication across the synapse is by means of chemicals called
neurotransmitters
IMPORTANCE OF A SYNAPSE
- 1 Neurotransmitters are only released from one side of the synapse
impulses move in one direction only
- 2 Ensures impulses are transmitted from a sensory neuron to a motor neuron
allows movement of impulses in one direction only
- 3 Prevents continuous stimulation of neurons
insignificant stimuli are filtered out to prevent overloading of the brain
HUMANS
HUMAN NERVOUS SYSTEM
Brain
CNS
Cranial nerves Central Nervous System
PNS
Peripheral nervous Spinal cord
system
Spinal nerves
THE FUNCTION OF THE NERVOUS SYSTEM
- 1 Detect changes in the environment and allow the body to react to stimuli
- 2 Enable co-ordination of various activities
3 TYPES OF NEURONS
1 SENSORY NEURON
- Carry impulses from receptors (nerve endings and sense organs) to the central
nervous system (CNS)
- Brain + spinal cord
2 MOTOR NEURON
- Carry impulses from the CNS to the effectors (muscle glands)
- The effectors bring about a response
3 INTERNEURON/CONNECTOR NEURON
- Link sensory neuron to motor neuron
- Carry impulses inside the CNS from a sensory neuron to a motor neuron
IMPULSE DIRECTION
Dendrite Cell body Axon
,DIAGRAMS OF 3 DIFFERENT TYPES OF NEURONS
SENSORY NEURON (Afferent)
Sensory receptor
Dendrite
Myelin sheath (outside membrane)
Cell body
Nucleus
Neurilemma
Axon branches / Axon terminal
MOTOR NEURON (Efferent)
Cell body
Nucleus
Dendrite
Neurilemma
Myelin sheath (outside membrane)
Axon branches
INTERNEURON (Connector)
Dendrite
Cell body
Nucleus
Axon branches
, NERVOUS TISSUE OF THE NEURONS
- The cell body has the following organelles:
- Nucleus
- Cytoplasm
- Mitochondria
- Ribosomes
- Endoplasmic reticulum
Dendrites
- Branching cytoplasmic threads
- Carry impulses towards the cell body
Axon
- Single long outgrowth which conducts impulses away from the cell body
Terminal branches
- Branch endings of the axon
Two membranes cover the axon
- 1 Myelin sheath
- provides electrical insulation
- speeds up the transmission of implants
- 2 Neurilemma
- encloses the myelin sheath
TRANSPORTATION OF NERVE IMPULSES
- More than 1 neuron is involved in the transport of nerve impulses
- Neurons are lined up so that the axon terminals of 1 neuron lay next to the dendrites
of another
- Neurons aren’t directly connected
- There is a microscopic gap (synapse) between the axon terminals of one neuron and
the dendrite of another
- Nerve impulses are carried along the neuron by electrical impulses
- Communication across the synapse is by means of chemicals called
neurotransmitters
IMPORTANCE OF A SYNAPSE
- 1 Neurotransmitters are only released from one side of the synapse
impulses move in one direction only
- 2 Ensures impulses are transmitted from a sensory neuron to a motor neuron
allows movement of impulses in one direction only
- 3 Prevents continuous stimulation of neurons
insignificant stimuli are filtered out to prevent overloading of the brain
