Term 2 Flashcards
Nervous System
Controls homeostasis through nerve impulses (action potentials) conducted along axons of neurons. At axon terminals, impulses trigger release of neurotransmitter molecules. The result is either excitation or inhibition of specific other neurons, muscle fibers (cells), or gland cells.
Nervous System
Types of cells of the nervous system
Neurons( Nerve cells) Neuroglia
Nervous System
Neurons (nerve cells) properties
Excitability: ability to RESPOND to a stimulus
Conductivity: ability to TRANSMIT a signal
Nervous System
Neuroglia properties
Specialized cells that support the neurons in some way
Ex. They phagocytize foreign substances, produce cerebrospinal fluid, and form myelin sheaths around axons
Nervous System organization
Central nervous system (CNS)
Peripheral nervous system (PNS)
Nervous system organization
Central nervous system (CNS)
Consists of the brain & spinal cord which are surrounded and protected by the skull and vertebral column respectively
May be thought of as the central control center of the body, receiving and interpreting or integrating all stimuli and relaying nerve impulses to muscles and glands where the designated actions take place
Nervous system organization
Peripheral nervous system
Includes all of the neural tissue outside the CNS. it delivers sensory information to the CNS and carries motor commands to peripheral tissues and systems.
Somatic nervous system (SNS)
Automatic (autonomic) nervous system (ANS)
Nervous system organization
Peripheral nervous system
Somatic nervous system
Division of the PNS composed of:
Somatic Afferent SENSORY division - which receives sensory information and conveys it to the spinal cord and brain via nerves.
Somatic Efferent MOTOR division - which regulates the contraction of skeleton via neuronal pathways that descend from the brain and spinal cord to lower motor neurons
Nervous system organization
Peripheral nervous system
Autonomic nervous system
Consists of sensory neurons that convey information from receptors in the viscera to the CNS and motor neurons from the CNS that conduct impulses to smooth muscle, cardiac muscle, and glands. Since its motor responses are not normally under conscious control, the ANS is involuntary.
Motor portion: sympathetic and parasympathetic division. With a few exceptions, the viscera receives instructions from both.
Sympathetic neurons - involve expenditure of energy
Parasympathetic neurons - restore and conserve body energy
Nervous System
Neurons - Three principled parts
The cell body
Dendrites
An axon
Nervous System
Neurons
Cell body
Vary in shape and size Has a large nucleus which contains a nucleolus, as well as several structures that are responsible for metabolism, growth and repair of the neuron - endoplasmic reticulum, lysosomes, mitochondria, neurofilaments, neurotubules, and Golgi apparatus
Neurofilaments: provide a skeletal framework for the axon
Neurotubules: function in the intracellular transport of the proteins and other substances, in both directions between the cell body and the ends of the processes
Nervous System
Neurons
Dendrites
Thread-like projections which are actually extensions of the cell body
Conduct nerve impulses towards the cell body
Nervous System
Neurons
Axons
A neuron generally has just one axon which extends from the cell body Carries nerve impulses away from the cell body to the next neuron, muscle or gland
Originates from the AXON HILLOCK
The initial segment, the site where the nerve impulse is initiated, lies immediately after the axon hillock
May have side processes called COLLATERAL BRANCHES end in a spray of small axon branches or TELODENRIA which end I tiny swellings called end bulbs
Nervous System
Neurons
Synapse
The junction between the end bulb of one axon and the cell body, dendrite, or axon of another neuron
A site where information is transferred from one cell to another
Ex. Neuron, muscle,gland
Nervous System
Neurons
Neurolemmocyte
Schwann cells
Form myelin sheaths around axons in the PNS
Nervous System
Neurons
Oligodendryte
Form myelin sheaths in the CNS
Nervous System
Myelination of axons
Some axons are covered with layers of a lipid sheath called myelin
Myelin sheath is formed by specialized non-neural cells called SCHWANN CELLS in the PNS and OLIGODENROCYTES in the CNS
The outer layer, or sheath, of the cells is the NEUILEMMA sheath
A myelin sheath is segmented, interrupted at regular intervals by gaps called NODES OF RANVIER. The distance between nodes is the INTERNODE.
There are myelinated and unmyelinated axons
A myelinated nerve fiber transmits a nerve impulse faster
Nervous System
Types of Neurons - Structural Classification
Multipolar Neurons
Have many processes consisting of many dendrites and a single axon
Ex. association (interneurons) and motor neurons
Nervous System
Types of Neurons - Structural Classification
Bipolar Neurons
have two processes: a dendrite and an axon which conducts action potentials to the CNS
Sensory neurons
Relatively Rare but play an important role in relaying information concerning sight, smell, and hearing
Nervous System
Types of Neurons - Structural Classification
Unipolar Neurons
Have one process, an axon Most sensory neurons are unipolar
Their peripheral ends have dendrite-like processes that respond to stimuli, producing action potentials that are conducted by the axon to the CNS
The branch that extends from the periphery to the neuron cell body, conducts action potentials to the cell body. According to a functional definition of a dendrite, it could be classified as a dendrite
Nervous System
The Reflex Arc - Location
Afferent Neurons
Convey information from the tissues and organs of the body to the CNS
Unipolar neurons are the most common in the PNS
Nervous System
The Reflex Arc - Location
Efferent or Motor Neurons
Convey nerve impulses away from the CNS to effectors (muscles and glands)
All motor neurons that control skeletal muscles are multipolar neurons
