The Nervous System And the Senses

Human Organ System Overview Nervous SystemIntegumentary SystemSkeletal SystemMuscular SystemCirculatory System

Human Organ System Overview (continued) Nervous SystemIntegumentary SystemSkeletal SystemMuscular SystemCirculatory System

Human Organ System Overview (continued) Nervous SystemIntegumentary SystemSkeletal SystemMuscular SystemCirculatory System

Human Organ System Overview (continued) Nervous SystemIntegumentary SystemSkeletal SystemMuscular SystemCirculatory System

Human Organ System Overview (continued) Nervous SystemIntegumentary SystemSkeletal SystemMuscular SystemCirculatory System

Human Organ System Overview (continued) Respiratory SystemDigestive SystemExcretory System Endocrine SystemReproductive SystemLymphatic System

The Nervous System Basic and smallest unit of nervous system is the neuron –The nervous system forms a communication and coordination network throughout an animal’s body. –Neurons are nerve cells that carry electrical signals from one part of the body to another.

Three Types of Neurons Sensory neurons – carry impulses from body to spinal cord and brain Motor neurons – carry response impulses away from brain and spinal cord to a muscle or gland Interneurons – found within the brain and spinal cord – connect sensory and motor neurons

The Neuron Neurons conduct impulses throughout nervous system and consists of three regions – cell body, dendrites, and axons –Dendrites – receive impulses and carry them to the cell body –Cell body – where nucleus of cell is –Axon – carries impulses away from cell body to other neurons, muscles, or glands

The Neuron Figure 27.2 Signal direction Dendrites Nucleus Cell body Signal pathway Synaptic terminals Supporting cell Myelin sheath Axon

Action Potential –A resting neuron has potential energy that can be put to work to send nerve signals from one part of the body to another. –This difference in charge (voltage) across the plasma membrane of a resting neuron is the resting potential. –A stimulus is any factor that causes a nerve signal to be generated. –A stimulus of sufficient strength can trigger an action potential, a nerve signal that carries information along a neuron. –If the stimulus is strong enough, a sufficient number of channels open to reach the threshold, the minimum change in a membrane’s voltage that must occur to trigger the action potential. –Action potential is like a “domino effect” along a neuron.

Action Potential Figure 27.3a Neuron interior Resting potentialA stimulus opens the first set of ion channels; if threshold is reached, an action potential is triggered. 12

Action Potential Figure 27.3b Additional channels open; in that region of the neuron, the interior of the cell becomes more positive than the outside. 34 The first set of channels closes and inactivates; a second set of channels opens and positive ions rush out; the membrane returns to resting potential.

Figure 27.4 Axon Action potential  1 23

Connections Between Neurons Neurons don’t touch one another – there is a tiny space between axons and dendrites called a synapse – need neurotransmitters (chemicals) to cross this gap and carry the “message” on

Connections Between Neurons Figure 27.5 SYNAPSE Synaptic terminal of sending neuron Dendrite of receiving neuron Sending neuron Vesicles Action potential arrives. Neuro- transmitter is released into synaptic cleft. Neuro- transmitter binds to receptor. Neurotransmitter molecules Ion channels Receiving neuron Synaptic cleft Synaptic terminal Vesicle fuses with plasma membrane. Neurotransmitter Receptor Ion channel opens and triggers or inhibits a new action potential. Ion channel closes. Neurotransmitter is broken down and released. Ions

Connections Between Neurons

Neurotransmitters

A Nerve Impulse

Central Nervous System (CNS) vs. Peripheral Nervous System (PNS) CNS – brain and spinal cord PNS – all nerves carrying “messages” to and from CNS –The vertebrate peripheral nervous system is divided into two functional components, the 1.motor system and 2.autonomic nervous system. –The motor system carries signals to and from skeletal muscles and mainly responds to external stimuli.

Central Nervous System (CNS) vs. Peripheral Nervous System (PNS) –The autonomic nervous system regulates the internal environment and controls –smooth and cardiac muscles and –organs and glands of the digestive, cardiovascular, excretory, and endocrine systems.

Parts of the Brain Cerebrum – thinking and learning center – conscious activities of the body Cerebellum – balance and coordination Medulla – involuntary activities

The Brain Pons Pituitary gland Hypothalamus Cerebrum Medulla oblongata Spinal cord Cerebellum Pineal gland Thalamus

The Senses Eyes – –Complex organ sensing light –Retina – thin layer of tissue made up of light receptors and sensory neurons –Two types of light receptor cells: Rods – detect shape and movement Cones – detect color

The Eye Choroid Retina Blood vessels Optic nerve Fovea Vitreous humor Sclera Ligaments Iris Pupil Cornea Aqueous humor Lens Muscle

Visual Problems –The most common visual problems are nearsightedness, the inability to focus well on distant objects, farsightedness, the inability to focus well on near objects, and astigmatism, blurred vision caused by a misshapen lens or cornea.

The Senses Ears – –Complex system detecting sound and helping to maintain a sense of balance/equilibrium

The Ear Auditory canal Tympanum Round windowEustachian tube Bone Cochlea Cochlear nerve Semicircular canals Oval window Stirrup Anvil Hammer

Hearing Problems –Deafness, the loss of hearing, can be caused by middle ear infections, injury, such as a ruptured eardrum, stiffening of the middle-ear bones (a common age- related problem), or overexposure to loud noises.