Nervous System Flashcards
What are the 2 main types of nervous system and what do they consist of?
- Central Nervous System - spinal cord, brain stem, brain
2. Peripheral Nervous System - autonomic and somatic NS
What are the 3 parts of the brain?
- Hindbrain
- Midbrain
- Forebrain
What does the Somatic NS control?
Voluntary processes
What does the Autonomic NS control and what are the 2 parts?
Involuntary processes
- Sympathetic NS (fight or flight)
- Parasympathetic NS (relaxes body)
Give 3 examples of involuntary processes
- Heart rate
- Digestion
- Respiration
Where is adrenaline produced?
Adrenal medulla
How does the somatic NS work?
Carries impulses to sensory organs in the CNS and relays motor commands to muscles
What are the 3 primary functions of the nervous system?
- Sensory input - sense environment inside and outside the body
- Integration - CNS integrates incoming sensory input
- Motor Output - CNS regulates and controls the body via motor system in response to sensory input
How many nerves does the Peripheral NS consist of?
31 pairs of spinal nerves
12 pairs of cranial nerves
What are the 2 divisions of the peripheral NS?
- Sensory nerve pathway
2. Motor nerve pathway
Describe the sensory nerve pathway
- Brings sensory information to the CNS from receptors in peripheral tissues and organs
- Transmits impulses via the spinothalmic tract
- Sensory decussation (crossing over) occurs within the spinal cord and medulla
- Tendons, muscles and joints have proprioceptors (nerve endings) which are stimulated by stretch
What is the difference between the afferent and sensory pathways?
Afferent = transmits impulses towards the brain Sensory = transmits impulses via the skin in response to pain
What does the motor nerve pathway include?
- Somatic NS - controls skeletal muscle contraction
- Autonomic NS - regulates smooth muscle, cardiac muscle, glands and adipose tissue
Describe the upper motor neurones
- Stimulus to contract joints originates in the cerebrum
- Upper motor neurones transmit this via extra-pyramidal tracts from the primary motor area of the cerebrum and pass via the internal capsule, pons and medulla; they decussate (cross over) at the medulla
- The upper motor neurones then travel to the spinal cord via the lateral corticospinal tract
What is the function of the lower motor neurone?
The final pathway that transmits impulses to skeletal muscles
Describe the pathway of an impulse from the CNS
CNS (brain and spinal cord) –> PNS (cranial and spinal nerves) –> Sensory (afferent) Nerves + Motor (efferent) Nerves
Describe the pathway of an impulse from the motor nerves
Motor (efferent) Nerves –> Somatic + Autonomic (Parasympathetic and Sympathetic)
Describe the effects of the sympathetic NS
- Stimulates and quickens effect on heart, circulatory and respiratory systems
- Dilation of pupils
- Inhibits peristalsis
- Inhibits saliva production
- Dilates bronchi
- Stimulates release of epinephrine and norepinephrine
Describe the effects of the parasympathetic NS
The same as sympathetic but opposite
What is dual innervation?
The sympathetic and parasympathetic NS working together to allow more precise control
Describe the activation of the Adrenal-cortical system in the fight-or-flight response
Hypothalamus activates the adrenal-cortical system –> Release of Corticotropin-releasing factor –> Activation of pituitary gland –> Release of Adrenocorticotropic hormone –> Activation of the adrenal cortex –> Release of 30 hormones into the bloodstream –> fight or flight
Describe the sympathetic NS action in the fight or flight response
- Activation of the adrenal medulla –> Epinephrine and Norepinephrine released into bloodstream –> fight or flight
- Activation of glands and smooth muscle –> fight or flight
Describe neurones
- Nerve cells
- React to chemical and sensory stimuli
- Conduct impulses
- Emit specific chemical regulators
What causes the release of neurotransmitters?
- Signal received
- Membrane potential changes
- Action potential initiated
- Axon terminals release neurotransmitters
What is the function of the dendrites?
Convey incoming messages towards the cell body
What is the function of the cell body?
Metabolic centre of the neurone that contains the nucleus
What is the axon hillock?
Beginning of the axon
What is the function of the neurofibrils?
Maintain cell shape
What is the function of the axon?
Transports impulses away from the cell body
What are the 3 functions of the neurone?
- Sensory (afferent) - carry impulses from sensory receptors to the CNS
- Motor (efferent) - carry impulses from CNS to muscles and glands
- Inter (association) - carry impulses between sensory and motor neurones
Describe the sensory nerves
- Somatic, cutaneous, common senses
- Proprioceptor senses (e.g. joint angle, muscle length, sense of self)
- Special sense (e.g. temperature, taste)
Where do sensory (afferent) nerves originate?
Organ glands and tissues
Describe the efferent nerves
- Spinal cord, brain, autonomic ganglia
- Transmit to effector organs (muscles and glands)
- Somatic = voluntary movement and reflex skeletal muscle contraction
- Autonomic - cardiac muscle, smooth muscle and glandular contraction
Describe the mixed (motor) nerves
- Outside spinal cord
- Sensory and motor nerves are enclosed in the same sheath of connective tissue
What are neuroglia cells?
- Divide continuously throughout life
- Support neurones by ensuring structural support, nourishment and protection
Name 6 neuroglia cells and their location
- Oligodendrocyte (CNS)
- Astrocyte (CNS)
- Ependymal (CNS)
- Microglia (CNS)
- Schwann cell (PNS)
- Satellite cell (PNS)
What is the function of oligodendrocytes?
Produce the myelin sheath
What is the function of astrocytes?
Barrier between capillaries and neurones
What is the function of ependymals?
Circulate cerebrospinal fluid to protect the CNS
What is the function of microglia?
Monitor the health of neurones and dispose of debris
What is the function of schwann cells?
Form the myelin sheath
What is the function of satellite cells?
Regulate diffusion of molecules into the cell body
What are the 2 major functional properties of nerve neurones?
- Irritability - the ability to respond to a stimulus and convert it into a nerve impulse
- Conductivity - the ability to transmit the impulse to neurones, muscles and glands
Describe a resting potential
- No impulse is initiated
- Membrane has different levels of K and Na on either side
- This results in an electrical charge difference of -70mV
- Na levels are higher in interstitial space and K higher inside the cell
- At rest, the voltage gates are shut and a pump mechanism moves the ions from high to low conc (Na moves in, K moves out)
Describe an action potential
- Allows impulse transmission
- Stimulus changes the permeability of the membrane to the ions which changes the membrane potential (inside more +ve, outside more -ve)
- Action potential moves along the neurone until it reaches the synapse between neurones
- Action potential spreads along neurones
Describe repolarisation
- K ions diffuse out of the cell as membrane permeability changes
- -Negative charge inside and +ve charge outside the membrane is restored
What is another word for the brain?
Encephalon
What is the diencephalon and what does it consist of?
The posterior part of the forebrain
- Thalamus
- Hypothalamus
- Epithalamus
- Pineal gland
Describe the thalamus
- Relays sensory impulses to the cerebral cortex
- Relays impulses between cerebral motor cortex and lower motor centres (lower and higher brain centres)
- Involved in memory
Describe the hypothalamus
- Centre of the autonomic NS
- Regulates temperature, food, water, hormonal output, sex, emotion, stress
- Produces ADH and oxytocin
Describe the midbrain
Contains visual and auditory reflex centres, subcortical motor centres and nuclei for cranial nerves III and IV
Describe the medulla oblongata
- Relays sensory impulses from skin to proprioceptors
- Controls HR, blood vessel diameter, respiratory rate and reflexes
- Site of crossover of pyramids
Describe the cerebral cortex
Extensive, wrinkled outer layer of the forebrain; governs higher brain functions, such as thinking, learning and consciousness
Describe the amygdala
Involved in fear and the discrimination of object necessary for organisms’ survival
What is the function of the hippocampus?
Involved in memory
What is the function of the pons?
Governs sleep and arousal
What is the function of the cerebellum?
Motor coordination
What is the reticular formation?
- An area in the pons
- Collection of neurones involved in arousal, stereotyped patterns (e.g. walking) and the sleep-wake cycle
What are the 3 major areas of the brain?
- Cerebrum = front area of brain, responsible for complex sensory and neural functions
- Brain Stem = midbrain, pons, medulla oblongata, responsible for the conduction of impulses and controls breathing, swallowing, HR, BP and consciousness
- Cerebellum = back area of brain, control essential body functions such as balance, posture and coordination
What are the meninges? Name the 3 layers
Membranous coverings of the brain and spinal cord.
- Dura Mater - 2 layers of dense fibrous tissue that covers the brain and spinal cord
- Arachnoid Mater - fibrous tissue separated from the dura mater by subdural space
- Pia Mater - protective layer separated from arachnoid mater by subarachnoid space
What is meningitis?
Inflammation of the meninges
What are the 3 types of myelinated nerve fibres?
- Transverse - interconnect the 2 hemispheres
- Projection - connect the cerebral cortex to the lower portion of the brain and spinal cord
- Association - connect various areas within the hemisphere
What are the names of the 4 lobes of the brain?
- Frontal
- Parietal
- Temporal
- Occipital
Describe the frontal lobe
Situated at the front of the cerebrum and is responsible for:
- Problem-solving
- Memory
- Language
Describe the parietal lobe
Situated at the top of the cerebrum and is responsible for:
- Touch
- Awareness of the body
- Interprets visual information
Describe the temporal lobe
Situated at the side of the cerebrum and is responsible for:
- Auditory receptive area
- Interpretative area
Describe the occipital lobe
Situated posteriorly in the cerebrum and is responsible for the visual receptive area
Name the 2 areas for speech
- Broca’s Area - responsible for speech; if it is damages, the victim is unable to say words properly
- Wernicke’s Area - responsible for comprehension of speech
What are the 5 constituents of cerebrospinal fluid?
- Water
- Glucose
- Oxygen
- Carbon dioxide
- Hormones and electrolytes
What are the 3 sources of cerebrospinal fluid?
- Choroid plexus (lines ventricles)
- Ependymal cells (occur in ventricles and meningeal blood vessels)
- Brain and spinal cord (blood vessels)
Describe the cerebrospinal fluid
- Forms a watery cushion that protects the brain
- Circulating volume = 150ml
- 600-700ml of CSF is formed per day
- Arachnoid mater provides drainage for CSF back into the blood via arachnoid villi/ granulation
How much does the brain weigh?
1400g
How is CSF secreted into the ventricles?
By the choroid plexus
Describe the relationship between movement of CSF and pressure differences on each side of the arachnoid villi
- High CSF pressure + Low venous pressure = CSF moves into bloodstream
- Low CSF pressure + High venous pressure = arachnoid villi/ valves shut down so CSF cannot move into bloodstream
Name the 4 cortexes of the brain
- Gustatory cortex (taste)
- Primary somatosensory cortex & Somatosensory association area (makes you aware of sensations)
- Primary visual cortex & Visual association area (vision)
- Primary auditory complex & Auditory association area (hearing)
Describe arterial circulation
- 2 vertebral + 2 internal carotid arteries supply brain with blood
- Vertebral arteries stem from subclavian arteries and join at the level of the pons to the basilar artery
- Basilar divides to form posterior cerebral arteries which supply the cerebellum
What do the vertebral arteries supply blood to?
- Cerebellum
- Brain stem
- Occipital lobes
- Inferior surface of temporal lobes
- Diencephalons
- Spinal cord
What do the internal arteries supply blood to?
- Majority of hemispheres (except occipital lobe)
- Basal ganglia
- Diencephalon
Describe venous circulation
- Vascular channels control cerebral venous drainage
- These are created in 2 dural layers called sinuses
- Extra cranial veins connect to the venous sinuses by emissary veins
- The brain and dural sinuses are connected by bridging veins
- The cerebral veins drain into the dural sinuses and then into the cranial veins
What is the blood-brain barrier?
- Provides protection by ensuring the NS is isolated from the rest of the body
- Ensure environment is optimal for neuronal function
Describe the movement of substances across the blood-brain barrier
- Dependent on size and electrical charge
- Controls movement of organic and inorganic ions
- Prevent peripheral neurotransmitters, metabolic waste and K entering the CNS
Describe the spinal cord
- Lies in the central canal and is formed by the bodies and neural arches of the vertebrae
- Consists of ganglia and nerve fibres
- Extends downwards from the medulla oblongata to the upper regions of the 2nd lumbar vertebrae
How many vertebrae are there in total?
33
What are ganglia?
Groups of neuronal cell bodies
What are the 2 main functions of the spinal cord?
- Links brain with nerves
2. Provides a centre for reflex action
Describe the grey matter
- Situated centrally in H shape, mainly on surface of brain
- Composed of neuronal cell bodies and unmyelinated axons
- Processes information in brain
- Also contains glial cells and capillaries
What are glial cells?
Transport nutrients and energy to the neurones and influence how well they function and communicate
(e.g. astroglia and oligodendrocytes)
Describe the white matter
- Situated in the inner layer of the cortex
- Composed of myelinated axons and very few neuronal cell bodies
- There are 31 pairs of spinal nerves
- Each group of nerve fibres are grouped into bundles/tracts
Name the 2 types of nerve tracts
- Lateralspinothalmic Tract - transmission of pain, temperature and touch from skin to thalamus
- Corticospinal Tract - fine motor control (face, mouth and hands)
How many pairs of cranial nerves are there?
12
What are the names of the 12 cranial nerves?
CNI - Olfactory CNII - Optic CNIII - Oculomotor CNIV- Trochlear CNV- Trigeminal CNVI- Abducens CNVII- Facial CNVIII- Vestibulocochlear CNIX- Glossopharyngeal CNX- Vagus CNXI- Spinal Accessory CNXII- Hypoglossal
What are the components needed for a reflex arc?
- Sensory neurones (sensory receptors to CNS)
- Relay/ Inter neurones (sensory neurones to motor neurones)
- Motor Neurones (CNS to muscle/gland)
How can bacteria enter the body to cause infection of the NS?
- Blood/bone
- Head injury
- Alimentary/ respiratory tract
- Surgical procedure
Give 5 examples of NS conditions
- Paraplegia
- Alzheimers
- Parkinsons
- Cerebral palsy
- Multiple sclerosis
