Neurons and Neural Anatomy

Nervous System Central nervous system (CNS): Brain Spinal cord Peripheral nervous system (PNS): Sensory neurons Motor neurons (somatic and autonomic)

The Nervous System The Nervous System Central Nervous System (CNS) Peripheral Nervous System (PNS) Brain Spinal Cord Motor Neurons Sensory Neurons Somatic Nervous System voluntary movements via skeletal muscles Autonomic Nervous System organs, smooth muscles Sympathetic - “Fight-or-Flight” responses Parasympathetic - maintenance

Divisions of the autonomic nervous system Rest Action Figure 3.20 on page 89 The sympathetic division of the nervous system prepares the body for action, whereas the parasympathetic returns it to a resting state.

Cells of the Nervous System There are 2 main kinds of cells Neurons Glial

Neurons Basic units (cells) of the nervous system Receive, integrate, and transmit information Operate through electrical impulses Communicate with other neurons through chemical signals

Glial cells 100 billion neurons 10x more glial cells Glial cells Support neurons (literally, provide physical support, as well as nutrients) Cover neurons with myelin Clean up debris Includes Schwann cells

Three main types of neurons

Three main types of neurons Sensory Neurons (peripheral N.S.) They transmit signals from the receptors to the central nervous system

Three main types of neurons Sensory Neurons (peripheral N.S.) They transmit signals from the receptors to the central nervous system Interneurons (or association neurons) (central N.S.) They process and integrate info to form a response

Three main types of neurons Sensory Neurons (peripheral N.S.) They transmit signals from the receptors to the central nervous system Interneurons (or association neurons) (central N.S.) They process and integrate info to form a response Motor Neurons (peripheral N.S.) Transmits the response from the CNS to effectors

Sensory (Afferent) vs. Motor (Efferent) sensory (afferent) nerve CNS e.g., skin Neurons that send signals from the senses, skin, muscles, and internal organs to the CNS motor (efferent) nerve CNS e.g., muscle Neurons that transmit commands from the CNS to the muscles, glands, and organs Gray’s Anatomy 38 1999

Structure of a Typical Neuron

The Reflex Arc (or withdrawal reflex) Figure 2.5B from: Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall.

Neural Anatomy Dendrite They receive messages from other neurons and conduct impulses toward the cell body

Neural Anatomy Dendrite Cell Body They receive messages from other neurons and conduct impulses toward the cell body Cell Body It determines if the signal will be inhibited or relayed

Neural Anatomy Dendrite Axon Cell Body They receive messages from other neurons and conduct impulses toward the cell body Cell Body It determines if the signal will be inhibited or relayed Axon It transmits the signal from the cell body to the axon terminal endings.

Neural Anatomy Dendrite Axon Cell Body Synapse They receive messages from other neurons and conduct impulses toward the cell body Cell Body It determines if the signal will be inhibited or relayed Axon It transmits the signal from the cell body to the axon terminal endings. Synapse The gap between axon terminals and dendrites

Neural Transmission

Neural Transmission Along The Axon Fatty material made by glial (Schwann) cells form the myelin sheath which insulates the neural transmission along the axon. The transmission along the axon is due to Na-K pumps embedded in the membrane. These pumps “fire” in succession and initiate an electrical impulse called an action potential (AP). In high speed transmission (Saltatory conduction), the impulse jumps gap to gap in the myelin sheath (Nodes of Ranvier).

Neural Transmission Along The Axon Figure 2.6 from: Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall. Source:

The 3 Functions of the Neuron 1. 3. 2. Figure 2.6 from: Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall. Source: Neurons = 3 functions: Reception, Conduction, Transmission

Action Potential (AP) Depolarization: The stimulus “threshold” is reached and the sodium-potassium pumps are activated and positively charged Na ions rush into to “fire” the pumps in succession.

Action Potential (AP) Repolarized: At maximum depolarization, the sodium gates close and the potassium gates open. Positively charged K ions rush out of the neuron. Refractory Period: The potassium gates close and, after a brief overshoot, resting membrane potential restored (~ 70 mV)

The Action Potential is like a “Wave”

How an Action Potential Works

Saltatory Conduction

Neural Transmission At The Synapse

Synaptic Transmission synaptic gaps = 1 millionth inch gap Impulses reaching the pre-synapse will release neurotransmitter (NT) from vesicles into the gap Figure 2.7 from: Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall. Source:

Synaptic Transmission NT crosses the synaptic gap and binds to receptors on the post-synaptic membrane to initiate an AP on post-synapse Enzyme in gap denatures NT Denatured NT returned to pre-synapse to be reassembled and packaged into vesicles. Impulse continues in the next neuron. Figure 2.7 from: Kassin, S. (2001). Psychology, third edition. Upper Saddle River, NJ: Prentice Hall. Source:

Examples of Neurotransmitters Receptor binding movie