Week 5 Content Flashcards
Functions of the Nervous System
- Sensory Input
- Integration
- Motor Output
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
Basic Divisions of the Nervous System
- Central Nervous System (CNS)
- Brain
- Spinal Cord - Peripheral Nervous System (PNS)
- Crainial Nerves
- Spinal Nerves
- Ganglia (Clusters of neuron cell bodies)
Basic Functions of CNS and PNS
Central Nervous System
- Integrates and commands all nervous system activity
Peripheral Nervous System
- Connects the body to the CNS
Sensory Input (Afferent)
Signals from sensory receptors
- PNS to CNS
Motor Output (Efferent)
Signals from CNS
- Muscles and Glands
Division by Body Region
- Somatic Sensory
- Senses information from body - Visceral Sensory
- Senses information from internal organs - Somatic Motor
- Controls muscle movement - Visceral Motor (Autonomic Nervous System)
- Controls involuntary movements (heart rate, digestion, etc)
Somatic
Body Structures
- Skin, muscles, joints
Visceral
Internal Organs
Functional Divisions of the PNS
Somatic Sensory Division (PNS)
General Senses: Widespread receptors in the body
- Touch
- Pain
- Vibration
- Pressure
- Temperature
Proprioception: Detects stretch in muscles and tendons
3 Types of Receptors
- Proprioceptors
- For body positioning - Cutaneous Receptors
- For touch, pressure, and temperature
Meisner Corpuscles: Detect fine touch deep in the dermis
Paxinian Corpuscles: Detects pressure and vibration
Ruffini Nerve Endings: Detects pressure and stretch
Free Nerve Endings: Sense pain and temperature
Merkel Discs: Detects light touch
Krause and Bulbs: Detects touch, more for pressure and stretching
Root Hair Plexus: For hair feeling
- Nociceptors
- For pain
Visceral Sensory Division (PNS)
Sensing things inside the body
- Stretch, pain, temperature, nausea, and hunger
Done through the digestive system, urinary system, and reproductive system
Vagus Nerve controls…
- Digestive system
Pelvic Nerve controls…
- Urinary and reproductive system
Somatic Motor Division (PNS)
Responsible for sending signals that make our skeletal muscles contract
- For voluntary control of muscle movement
Visceral Motor Division (PNS)
Controls the contraction of our smooth muscles, cardiac muscle, and visceral organs
- ie; digestion, heart rate
Part of Autonomic Nervous System
- Involuntary
Nervous Tissue
Densely packed
Neurons (Nerve cells): Transmit electrical signals
Glia: Support cells, non-excitable; surround and protect neurons
Glia of the CNS
Astrocytes
- Support neurons, maintain blood brain barrier
Microglia
- Immune cells of the brain
Ependymal Cells
- Make cerebral spinal fluid
Oligodendrocytes
- Form myelin sheaths around the neurons
Glia of the PNS
Schwann Cells
- Surround axons of the myelin sheath
Satellite Cells
- Support and protect the ganglia
Neurons
Basic unit of the nervous system
- Special nerve cells that conduct electrical impulses (action potentials)
- Can last a lifetime
- High Metabolic Rate: Require oxygen and glucose; die after 5 minutes
Non-dividing cells
- Precursor cells are neural stem cells (regenerative cells)
Cell Body (Soma)
Main structural component of neurons
- 5 to 140 um in size
- Contains organelles and unique structures
Neurofibrils: Bundles of intermediate filaments that form a network
Most cell bodies are in the CNS
- Form ganglia in the PNS
Neuron Processes (From Cell Body)
- Axons
- Dendrites
- Axon Branching
Dendrites
Branch extensively from the cell body
- Receive signals from other neurons
- Transmit signals towards the cell body
Axons
Only one per neuron
- Transmit impulses away from the cell body
- Axon Helix generates electrical impulses
- Neurofilaments, actin, and microtubules support the axon and aid in axonal transport
Axon Branching
- Axon Collaterals
- Infrequent branches - Terminal Arborization
- Multiple branches at the end, ending in terminal boutons
Nerve Impulse
- Generated at the axon hillock
- Conducted to the terminal boutons (branches at end of axon)
- Vesicles release neurotransmitters into synapse
Synapse
Where neurons communicate
- Most signals passed through chemical signals
- Electrical transmission of some signals through gap junction
Presynaptic Neuron
Transmits toward the synapse
Postsynaptic Neuron
Transmits away from the synapse
Functional Classification of Neurons
- Sensory Neuron
- Motor Neuron
- Interneuron
Sensory (Afferent) Neurons
Transmit impulses towards the CNS
- Cell bodies in ganglia outside the CNS
Processes
- Central: Terminates in the CNS
- Peripheral: Extends from sensory receptors
Motor (Efferent) Neurons
Carry impulses away from the CNS to effector organs
- Cell bodies in the CNS
- Form junctions with effector cells
Interneurons (Association Neurons)
Located between motor and sensory neurons
- Only in CNS
- Relay information between these neurons
Myelin Sheaths
Composed of the lipoprotein myelin
- Surrounds thicker axons
- Prevents current leakage and increase conduction speed
Nodes of Ranvier: Gaps along axons
- Speed up signal transmission
Myelin Sheaths in the PNS
Formed by Schwann cells
- Wrap around axons in concentric layers
Myelin Sheaths in the CNS
Formed by oligodendrocytes
- Coil around multiple axons (3-50 at one time)
Gray Matter
Neurons that aren’t myelinated
- Contain neuron cell bodies, dendrites, short nonmyelinated neurons, and neuroglia
Surrounds central cavities of the CNS
- Site of synapses
Dorsal Horn: Interneuron cell bodies
Ventral Horn: Motor neuron cell bodies
White Matter
Myelinated Neurons
- Axons connect regions of the CNS
Tracts: Bundles of axons traveling to similar destinations
Nerves
Cable-like organs in the PNS
- Connect the brain and the spinal cord to the rest of the body
Many axons wrapped in connective tissue
- Myelinated (Schwann Cells) and non-myelinated
- Sensory and motor
Components of the Nervous System
Neuronal Integrations
PNS Nerves
- Afferent Fibers: Pick up sensory signals and send them to the CNS
- Efferent Fibers: Carry signals from the CNS to muscles and glands
CNS Nerves
- Interneurons: Receive and send sensory nervous system to CNS
- Initiate motor responses
Reflex Arcs
Simple chains of neurons responsible for reflexes
- Rapid, autonomic motor responses (visceral or somatic)
Reflex Arc Components
- Receptor: Detects stimulus
- Sensory Neuron: Transmits afferent impulses to the CNS
- Integration Center: One or more synapses in the CNS
- Motor Neuron: Sends efferent impulses to the effector
- Effector: Muscle or gland that responds (contracts or secretes)
Monosynaptic Reflex
Fastest and simplest type of reflex
- Only one synapse involves
- No interneurons involves
- ie; Knee-jerk reflex
Polysynaptic Reflex
More common reflex, involves one or more interneurons
- Interneurons relay signals to motor neurons
- ie; Withdrawal reflex
Rostral
Toward the nose
Caudal
Toward the tail
Brain Functions
Controls heart rate, respiratory rate, and blood pressure
Regulates the autonomic nervous system and endocrine system
Controls head movements and sensations via cranial nerves
Brain - Higher Cognitive Processes
Intelligence
Consciousness
Memory
Sensory-motor integration
Emotion
Behavior
Socialization
Basic Parts of the Brain
Brain Stem: Midbrain, pons, and medulla
Cerebellum
Diencephalon
Cerebrum: Two hemispheres
Ventricles
Fluid-filled cavities within the brain, contain cerebrospinal fluid (CSF)
Lateral Ventricles
Cerebral hemispheres, 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 the central canal of the spinal cord
Distribution of Gray and White Matter
Gray Matter: Central, contains neuronal cell bodies
White Matter: External, consists of axons
Cortex: Outer layer of gray matter in the cerebrum and cerebellum
Brain Stem Functions
Pathway for fiber tracts between the cerebrum and spinal cord
Facial and head innervation (10/12 cranial nerves)
Controls automatic survival behaviour
Integrates auditory and visual reflexes
Midbrain
Between the diencephalon and pons
Cerebral Aqueduct: Central cavity for CSF flow
Cerebral Peduncles: Ventral tracts for motor commands (corticospinal)
Superior Cerebellar Peduncles: Link midbrain to cerebellum
Other Midbrain Structures
Periaqueductal Gray Matter: Fight or flight responses, pain modulation
Corpora Quadrigemina
- Superior Colliculi: Visual reflexes
- Inferior Colliculi: Auditory reflexes
Pigmented Nuclei
- Substantia Nigra: Produces dopamine, linked to motor control
- Red Nucleus: Coordinates limb movement
Organization of the Midbrain
Tectum: Above the cerebral aqueduct, includes the superior and inferior colliculi (Sensory processing and reflexes)
Tegmentum: Below the cerebral aqueduct, includes the red nucleus, substantia nigra, and reticular formation (Motor control, arousal, movement, and sleep)
Midbrain Innervation
III - Oculomotor Nerve
IV - Trochlear Nerve
Pons
Bridge between the midbrain and medulla oblongata
Motor tracts from the cerebral cortex
Pontine Nuclei: Connects the cortex to the cerebellum via middle cerebellar peduncles
Pons Innervation
V - Trigeminal Nerve
VI - Abducens Nerve
VII - Facial Nerve
Medulla Oblongata
Caudal part of the brainstem, continuous with the spinal cord
- Contains reticular formation
Autonomic Centers: Cardiac, vasomotor, and respiratory regulation
Hiccupping, sneezing, swallowing, and coughing
Medulla Oblongata - Major Structures
Pyramids: On ventral surface
Decussation of the Pyramids: Crossing over of motor tracts
Inferior Cerebellar Peduncles: Fiber tracts connecting the medulla and cerebellum
Olive: Contains inferior olivary nucleus
Medulla Oblongata Innervation
VIII - Vestibulocochlear Nerve
IX - Glossopharyngeal Nerve
X - Vagus Nerve
XII - Hypoglossal Nerve
Cerebellum - Functions
Dorsal (back) to pons and medulla
Coordinates body movements
Controls posture, balance, and fine motor movement
Cerebellum - Higher Cognitive Functions
Motor Tasks
Working Memory Task
Emotion Processing Task
Social Processing
Language Processing
Cerebellar Hemispheres
Surface folded into ridges called folia
- Separated by fissures
Subdivisions
1. Anterior Lobe
2. Posterior Lobe
3. Flocculonodular Lobe
Cerebellar Regions
- Cortex (Gray Matter)
- Arbor Vitae (Internal White Matter)
- Deep Cerebellar Nuclei (Deep Gray Matter)
Cerebellar Cortex Functions
Input from…
1. Equilibrium Sensors
2. Cerebral Cortex
3. Sensory Receptors (Limbs, neck, and trunk)
Compares intended movement with body position
- Adjust and fine-tune motor commands
Cerebellar Peduncles
Superior, Middle, and Inferior Peduncles
- Thick tracts connecting the cerebellum to the brain stem
Ipsilateral Pathways: Fibers travel to and from the same side of the body
Diencephalon
Core of the forebrain, surrounded by cerebral hemispheres
3 Paired Structures
1. Thalamus
2. Hypothalamus
3. Epithalamus
Borders the third ventricle
Primarily gray matter
Thalamus
80% of Diencephalon
- 12 major nuclei
Relay station for sensory signals to the cerebral cortex
Afferent impulses synapse in the thalamic nuclei
Nuclei amplify or tone down signals
Hypothalamus
Between the optic chiasm and the mamillary bodies
Pituitary gland projects inferiorly
Contains 12 nuclei
Main visceral control center of the body
Hypothalamus Functions
4 F’s
Fight: Behaviour and control of emotional responses
Flight: Emotions responses and ANS control
Feeding: Hunger and thirst
Fornicating: Sexual behaviour, endocrine system
Other: Body temperature, sleep-wake cycles, memory formation
Epithalamus
Located at the roof of the third ventricle
Contains small nuclei, including the pineal gland
- Secretes melatonin, regulated by the hypothalamus
Role in controlling circadian rhythms
Cerebrum
83% of the Brain’s Mass
Fissures: Deep grooves
Longitudinal Fissure: Divides hemispheres
Transverse Fissure: Separates cerebrum and cerebellum
Features of the Cerebral Cortex
Cortex: Outermost layer of the cerebrum, gray matter
Sulci: Grooved indentations
Gyri: Raised ridges
Increase surface area of the cerebral cortex
Form brain divisions
Deep Sulci
Divide cerebrum into lobes
- Lobes named after overlying skull bones
Central Sulcus separates the frontal and parietal lobes
- Bordered by 2 gyri (Precentral and Postcentral Gyrus)
Central Hemispheres - Key Features
Parieto-occipital Sulcus: Separates occipital and parietal lobes
Lateral Sulcus (Sylvian Fissure): Separates temporal from parietal and frontal lobes
Insula: Deep within the lateral sulcus
Lobes of the Cerebral Cortex
- Frontal Lobe
- Parietal Lobe
- Occipital Lobe
- Temporal Lobe
- Insular Lobe
Frontal Lobe
Rostral Brain
Involved in motor control, planning, reasoning, and decision-making
Parietal Lobe
Caudal to the frontal lobe
Involved in sensory processing, spatial awareness, and perception
Occipital Lobe
Caudal Brain
Responsible for visual processing
Temporal Lobe
Inferior to frontal and parietal lobes
Involved in auditory processing, memory, and language comprehension
Insular Lobe
Deep within the lateral sulcus
Plays a role in emotion, self-awareness, and taste
Cerebral Cortex
Gray Matter
- Neuronal cell bodies, dendrites, and short axons
Folds increase surface area
40% of brain mass
Brodmann Areas: 47 distinct regions
Cerebral Cortex Functions
Home of consciousness
- Awareness of self and sensations
- Control of voluntary movements
Communication, memory, and understanding
