Human Systems:Nervous System& Sense Organs

Nervous system

The nervous system

• Need for communication

• Communication is required for coordination

• Gather information• Process information• Respond accordingly

The nervous system

• Nervous system has two parts (central and peripheral)– Central nervous system (CNS) – brain and spinal cord– Peripheral nervous system (PNS) – other parts of the nervous system

• The CNS processes and responds to all messages coming from the peripheral nervous system

• The PNS connects all parts of the body to the CNS• It uses specialized structures called nerves to carry

information between body and CNS

The nervous system

Neurons

• Nervous system is made up of cells known as nerve cells or neurons

• Cell body, axon and dendrites• Nerve cells are connected to each other

Nerves

• A nerve is a collection of axons bundled together with blood vessels and connective tissue

• Nerves are found everywhere in the PNS

• Most nerves have axons of both sensory neurons and motor neurons

Nerves

Peripheral nervous system

• Sensory neurons – gather information• Special nerve endings called as receptors

• Motor neurons – send impulses from brain and spinal cord to other parts of the body e.g. muscle, sweat glands etc.

Peripheral nervous system

• PNS has two types of motor neurons – somatic and autonomic

• Somatic - under conscious control (voluntary movements such as writing, talking, smiling, or jumping)

• Autonomic - controls body functions that you do not think about, such as digestion and heart rate – Maintain body’s functions in balance– Depending on the situation, the autonomic nervous system can speed

up or slow down these functions– The autonomic nervous system has two divisions: the sympathetic

nervous system and the parasympathetic nervous system

Peripheral nervous system

Central nervous system

• The central nervous system receives information from the sensory neurons

• Then it responds by sending messages to the body through motor neurons in the PNS

• Made up of brain and spinal cord

Brain

• Largest organ in the nervous system• Different parts perform different functions

• Cerebrum– Largest part of the brain– Controls voluntary movements– It also allows to sense touch, light, sound, odors, taste, pain, heat etc.– The cerebrum is made up of two halves, called hemispheres.– The left hemisphere directs the right side of the body, and the right

hemisphere directs the left side of the body

Brain

Brain

• Cerebellum– The second largest part of your brain and lies

beneath the back of the cerebrum– The cerebellum processes sensory information

from the body, such as from skeletal muscles and joints

– This allows the brain to keep track of the body’s position

Brain

• Medulla– The medulla connects brain to the spinal cord– Controls involuntary processes such as involuntary breathing,

the regulation of blood pressure and heart rate– Medulla constantly receives sensory impulses from receptors in

blood vessels and uses this information to regulate blood pressure

– The medulla also sends impulses to the heart to make the heart beat faster or slower

Brain

Spinal cord

• Spinal cord– It is made of neurons and bundles of axons that pass impulses to

and from the brain– The spinal cord is surrounded by protective bones called

vertebrae – The axons in spinal cord allow the brain to communicate with

PNS– The axons of sensory neurons in skin and muscles carry

impulses to the spinal cord– The spinal cord relays these impulses to the brain– The brain interprets these impulses as pain, temperature, or

other sensations and responds to the situation

Spinal cord

Spinal cord

• Spinal cord injury– May block information flow to and from the brain– Paralysis

Sense organs

Sense of touch

• Skin – integumentary system (which includes hair, skin, nails)• Protect body from damage• Glands and receptors

• Reflex

• Skin and feedback mechanism (Body temperature)

Sense of sight

• Eyes detect light and brain forms visual images• Cornea and retina• Mechanism of vision

Sense of sight

• Reacting to light – role if iris• Focusing light

Sense of hearing

• Sound and vibrations• Ear – outer, middle and inner• Outer ear

– Pinna and ear canal

• Middle ear– Tympanic membrane or ear drum– Bones (hammer, anvil and stirrup)

• Inner ear– Cochlea and auditory nerve– Fluid and balancing body

Sense of hearing

Sense of taste

• Taste is the sense that detects chemicals and to distinguish flavors

• The tongue is covered with tiny bumps called papillae which contain taste buds

• Taste buds contain clusters of taste cells, the receptors for taste . They respond to dissolved-food molecules

• Taste cells react to five basic tastes: sweetness (sugar), sourness (lemon), saltiness (salt), savoriness (meats and cheeses), and bitterness (some medicines)

• When the brain combines information from all of the taste buds, you taste a “combination” flavor

Sense of taste

Sense of smell

• The receptors for smell are located on olfactory cells in the upper part of your nasal cavity

• An olfactory cell is a nerve cell that responds to chemical molecules in the air. You smell something when the receptors react to molecules that have been inhaled

• The molecules dissolve in the moist lining of the nasal cavity and trigger an impulse

• Olfactory cells send those impulses to the brain, which interprets the impulses as odors

• Taste buds and olfactory cells both detect dissolved molecules• The brain combines information from both senses to give

sensations of flavor.

Sense of smell