Anatomy (Everything but muscles and bones)

Sensory Input

Detects stimuli inside and outside the body using sensory receptors

Integration

Processes and interprets sensory input to determine a response

Motor Output

Activates effector organs (muscles/glands) to produce a response

CNS consists of…

Brain and spinal cord

PNS consists of…

Ganglia, Cranial and Spinal nerves

Ganglia

Clusters of neuron cell bodies

Sensory Input (Afferent)

Signals from sensory receptors; from PNS to CNS

Motor Output (Efferent)

Signal from CNS to muscles and glands

Somatic Body Region

Body structures like skin, muscle and joints

Visceral Body Region

Internal organs

4 Divisions By Body Region

1. Somatic Sensory

2. Visceral Sensory

3. Somatic Sensory

4. Visceral Motor (ANS)

Somatic Sensory includes…

General senses, proprioception and special senses

Somatic Sensory: General Senses

Widespread receptors in the body like touch, pain, vibration, pressure and temperature

Somatic Sensory: Proprioception

• Detects stretch in muscles and tendons

• Awareness of body position and movement

Somatic Sensory: Special Senses

Vision, hearing and balance

Visceral Sensory includes…

General and special senses

Visceral Sensory: General Senses

• Stretch, pain, temperature, nausea, and hunger

• Digestive, urinary, and reproductive organs

Visceral Sensory: Special Senses

Taste and smell

Somatic Motor

• Controls skeletal muscle contraction

• Voluntary movement; somatic nervous system

Visceral Motor

• Controls smooth muscle, cardiac muscle, glands, and organs

• Involuntary regulation like sneezing and coughing; ANS

Nervous Tissue

• Densely packed

• Includes neurons and glia

Glia

Support cells, non-excitable; surround and protect neurons

Neurons

• Conduct and transmit electrical impulse and signals

• Last a lifetime

• Non-dividing (except neural stem cells)

• High Metabolic Rate: Require O2 and glucose or they die after 5 minutes

Cell Body (Soma)

• Contains organelles and unique structures

• Neurofibrils - Bundles of intermediate filaments; form a network

• Mostly in the CNS

• Form ganglia in the PNS

Neuron Processes

• Axons

• Dendrites

• Axon Branching

Dendrites

• Branch extensively from the cell body

• Receive signals from other neurons

• Transmit signals toward cell body

Axons

• Only one per neuron

• Transmit impulses away from the cell body

• Neurofilaments, actin, microtubules provide strength and aid in axonal transport

Axon Branching

• Axon Collateral - Large infrequent branches

• Terminal Arborization - Multiple branches at the end, ending in terminal boutons; small

Nerve Impulse

• Generated at the initial segment of the axon (axon hillock)

• Conducted to the terminal boutons

• Vesicles release neurotransmitters into synapse

Synapse

Where most neurons communicate either by signals through chemical messengers and some via gap junctions

Presynaptic Neuron

Transmits toward synapse

Postsynaptic Neuron

Transmits away from the synapse

Sensory Neuron

• Afferent neurons transmit impulses toward the CNS; arrive

• Central processes terminate in the CNS

• Peripheral processes extend from sensory receptors

Motor Neurons

• Efferent neurons that carry impulses away from the CNS to effector organs

• Cell bodies in the CNS

• Form junctions w/ effector cells

Interneurons

• Association neurons

• Located b/w motor and sensory neurons

• Only found in the nervous system, confined to CNS

• Relay signals to motor neurons

Myelin Sheaths

• Surround and insulate thicker axons

• Prevents current leakage and increases conduction speed

Nodes of Ranvier

Gaps along axons

Myelin Sheaths in PNS

• Formed by Schwann cells

• Wrap around axons in concentric layers

Myelin Sheaths in CNS

• Formed by oligodendrocytes

• Coil around multiple axons

Gray Matter

• Surround central cavities of the CNS

• Contain neuronal cell bodies, dendrites, short nonmyelinated neurons, and neuroglia

• Sites of synapse

Gray Matter: Dorsal

Interneuron cell bodies

Gray Matter: Ventral

Motor neuron cell bodies

White Matter

• External to gray matter

• Consists of myelinated and nonmyelinated axons

• Axons connect regions of the CNS

White Matter: Fibre Tracts

Bundles of axons traveling to similar destination

Nerves

• Cable-like organs in the PNS

• Many axons wrapped in connective tissue:

  • Myelinated (Schwann cells) and nonmyelinated

  • Sensory and motor

Neural Integration: PNS Nerves

• Afferent fibres respond to sensory stimuli

• Efferent fibres transmit motor signal to muscles and glands

Neural Integration: CNS Nerves

• Interneurons

• Receive sensory input

• Direct information to CNS regions

• Initiate motor responses

Reflex Arcs

• Simple chains of neurons responsible for reflexes

• Rapid, autonomic motor response (visceral or somatic)

Reflex Arc: Receptor

Detect stimulus

Reflex Arc: Sensory Neurons

Transmits afferent impulses to the CNS

Reflex Arc: Integration Center

One or more synapses to the effector

Reflex Arc: Motor Neuron

Sends efferent impulses to the effector

Reflex Arc: Effector

Muscle or gland that responds (contract or secretes)

Monosynaptic Reflex

• Simplest and fastest reflex w/ only one synapse

• Ex: Knee-jerk reflex

Polysynaptic Reflex

• More common reflex, involves one or more interneurons

• Ex: Withdrawal reflex

Rostral

Toward the nose; forward

Caudal

Toward the tail of spine; back

Basic Parts and Organization of The Brain

• Brain Stem

• Cerebellum

• Diencephalon

• Cerebrum

Ventricles

4 fluid-filled cavities within the brain, contain cerebrospinal fluid (CSF)

Lateral Ventricles

Cerebral hemisphere, horseshoe-shaped

Third Ventricle

Diencephalon, connected to lateral ventricles by the interventricular foramen

Cerebral Aqueduct

Connects the third and fourth ventricles

Fourth Ventricle

Hindbrain, connects to central canal of spinal cord

Cortex

Outer layer of gray matter in cerebrum and cerebellum

Brain Stem consists of…

• Midbrain

• Pons

• Medulla

Brain Functions include…

• Vital control and regulation

• Higher cognitive processes

Brain Stem Functions

• Pathway for fiber tracts b/w cerebrum and spinal cord

• Facial and head innervation

• Controls automatic survival behavior

• Integrate auditory and visual reflexes

Midbrain

• B/w the diencephalon and pons

• Includes: Cerebral Aqueduct, Cerebral Peduncles and superior cerebellar peduncles

Cerebral Aqueduct

Central cavity for CSF flow

Cerebral Peduncles

Ventral tracts for motor commands (corticospinal)

Superior Cerebellar Peduncles

Link midbrain to cerebellum

Periaqueductal Gray Matter

Fight-or-flight responses, pain modulation

Corpora Quadrigemina

• Big nuclei that splits into superior and inferior colliculi

Superior Colliculi

Visual reflexes

Inferior Colliculi

Auditory reflexes

Substantia Nigra

Produces dopamine, linked to motor control

Red Nucleus

Coordinates limb movement

Midbrain: Tectum

Above cerebral aqueduct, includes superior and inferior colliculi, and is involved in sensory processing and reflexes

Midbrain: Tegmentum

Below cerebral aqueduct, includes red nucleus, substantia nigra, and reticular formation

Midbrain Innervation

• 3 Oculomotor nerve

• 4 Trochlear nerve

Pons

• Bridge b/w midbrain and medulla oblongata

• Allows motor tracts from cerebral cortex reach targets

Pontine Nuclei

Connects cortex to the cerebellum via middle cerebellar peduncles

Pons Innervation

• 5 Trigeminal nerve

• 6 Abducens nerve

• 7 Facial nerve

Medulla Oblongata

• Caudal part of brainstem, continuous w/ spinal cord

• Contains reticular formation and projection fibers

Medulla Oblongata Autonomic Centers

Cardiac, vasomotor, and respiratory regulation

Medulla Oblongata Role

Hiccupping, sneezing, swallowing, and coughing

Medulla Oblongata: Major Structure - Pyramids

Large triangular structures on ventral surface

Medulla Oblongata: Major Structure - Decussation of the Pyramids

Crossing over of motor tracts (carry movement commands from the brain to the spinal cord)

Medulla Oblongata: Major Structure - Olive

Contains inferior olivary nucleus

Medulla Oblongata Innervation

• 8 Vestibulocochlear nerve

• 9 Glossopharyngeal nerve

• 10 Vagus nerve

• 11 Hypoglossal nerve

Cerebellum

• Dorsal to pons and medulla

Cerebellum Regulatory Functions

• Coordinates body movements

• Controls posture, balance and fine motor movement

Cerebellum Higher Cognitive Functions

• Motor tasks

• Working memory tasks

• Emotion processing

• Social processing

• Language processing

Cerebellar Hemispheres

• Surface folded into ridges called folia and separated by fissures

• Subdivided into: anterior, posterior and flocculonodular lobes

Cerebellar Regions

• Cortex (gray mater)

• Arbor Vitae (internal white matter)

• Deep Cerebellar Nuclei (deep gray matter)

Cerebellar Cortex Functions

• Compares intended movement w/ body position

• Adjust and fine-tune motor commands

Cerebellar Cortex Input

• Equilibrium sensors

• Cerebral cortex

• Sensory receptors (limbs, neck, and trunk)

Cerebellar Peduncles

• Superior, Middle, and Inferior Peduncles are thick tracts connecting the cerebellum to brain stem

• It is an ipsilateral pathway

Ipsilateral Pathway

Fibers travel to and from the same side of the body

Diencephalon

• Core of forebrain, surrounded by cerebral hemispheres

• Contains 3 paired structures: Thalamus, hypothalamus, and epithalamus

• Border the third ventricle

• Primarily gray matter