Biol 216- chapter 6- the nervous system

Evolution of nervous system: 

• Invertebrates have simpler nervous system- fewer neurons and less complex networks

• Cephalization: concentration of sensory organs, and nervous tissue in the head, leading to more sophisticated nervous systems

• Nerve nets, Bilateral symmetry – better coordination and movement

Vertebrate nervous system:

• Neural tube formation: leads to development of CNS, with neural crest cells differentiating into various cell types

• Gene expression: ensures proper cell differentiation

Brain functions: 

• Receiving information

• Integrating information

• Storing information

• Sending out information

Key structures: 

• Blood brain barrier: protects the brain by restricting access to large molecules and microscopic objects, allowing essential small molecules like oxygen and glucose to pass.

• Meninges: connective tissue layers that cover the brain and spinal cord, providing structural support and protection. 

• CSF: circulates through the brain and spinal cord, providing nutrients and cushioning the brain.

• Ventricular system: cavities filled with CSF that protect the brain from injury.

  • 2 lateral ventricles

  • Third ventricle

  • Fourth ventricle

Brain anatomy: 

• Forebrain: 

  • Forms cerebrum- has left and right hemispheres

  • Cerebral hemispheres: 

    • Left hemisphere: focus on details, spoken and written language, abstract reasoning, math

      • Brocas and wernickes 

    • Right hemisphere: focus onboard background, relative position of objects, intuitive thinking, conceptualization, music, art

    • Lateralization: difference in function between the left and right hemisphere 

• Cerebral cortex: 

  • Outermost thin later of gray matter covering a core of white matter

    • Grey matter: neuron cell bodies and dendrites

    • White matter: axons

  • Convoluted to increase surface area

  • Regulates cognitive functions, such as thinking, learning, speaking, remembering, and making decisions

  • Has areas that: 

    • Primary somatosensory area: Receive and integrate sensory information 

    • Primary motor area: are involved in the planning, control, and execution of voluntary movements 

    • Association areas: integrate sensory information, formulate responses, relay responses to motor area

      • Brocas, wernickes

• Cerebrum

  • Frontal lobe

    • Executive function

  • Parietal lobe

    • Behind frontal lobe

    • Deals with perception and integration of stimuli from the senses

  • Occipital lobe

    • Back of brain

    • Concerned with vision

  • Temporal lobe

    • Long the side of the brain under the frontal and parietal lobes

    • Deals with senses of smell, sound, and the formation and storage of memories

• Cerebellum

  • Coordinates and refines body movements by information integration and comparison

  • Receives sensory information from: 

    • Receptors in muscles and joints

    • Balance receptors in the inner eat

    • Touch, vision and hearing receptors

  • Information about body position, the directions of movement of limbs or trunk

  • Compares sensory input with signals from the cerebrum that control voluntary body movements

• Brain stem

  • Structures: 

    • Medulla

    • Pons

    • Midbrain

      • Smallest region of the brain

      • Acts as relay station for auditory and visual information

      • Controls eye movement

      • Ventral tegmental area- VTA

        • Dopamine and serotonin producing neurons

        • Involved in pleasure pathway/reward circuit

      • Substantia nigra

        • Control of body movement

        • Contains dopamine-producing neurons

        • Degeneration of neurons in the substantia nigra is associated with Parkinson's disease

  • connect forebrain with spinal cord

  • Functions: 

    • Heart and respiration rate

    • Blood pressure

    • Blood vessel dilation

    • Digestive system reflexes- vomiting 

  • Reticular formation: 

    • Network of neurons in the brain stem that connect the thalamus to the spinal cord

    • Integrate incoming sensory information

    • Filters incoming information 

    • Ascending reticular formation

      • Sends stimulatory signals to the thalamus to activate the cerebral cortex

      • Produces different levels of alertness or consciousness

      • Footers incoming stimuli to discriminate irrelevant background stimuli

      • abnormalities- comatose

    • Descending reticular formation

      • Receives information from the hypothalamus

      • Connects with interneurons of the spinal cord that control skeletal muscle contractions

• Thalamus

  • Structure between the cerebral cortex and midbrain

  • Function: relaying signals from the special sense and motor signals to the cerebral cortex

  • Regulates consciousness, sleep and alertness

• Hypothalamus

  • Below thalamus, above brainstem

  • Synthesizes and secrets neurohormones

  • Links nervous and endocrine systems via pituitary gland

  • Controls body temperature, hunger, thirst, fatigue, circadian cycles

  • Trigger swearing, shivering

  • Monitors the osmotic balance of the blood 

• Basal nuclei/ basal ganglia

  • Group of nuclei of varies origin in the brains of vertebrates that act as a cohesive functional unit

  • Contains substantia nigra

  • Surrounds thalamus

  • Involved with voluntary movement

  • Damage causes Parkinson’s disease

• Limbic system

  • Called emotional brain

  • Parts of thalamus, hypothalamus, basal nuclei

  • Amygdala- emotion, fear

  • Hippocampus- memory

  • Olfactory bulbs- smell 

  • Hippocampus

    • Part of the limbic system

    • Consolidation of information from short to long term memory and spatial navigation

    • Alzheimer’s- hippocampus is the first to suffer damage

      • Memory loss

      • Disorientation

The reward pathway

• VTA secretes dopamine

• Nucleus accumbens contains dopamine sensitive cells

• Causes feelings of pleasure

• Amygdala and hippocampus play roles in memory, and deciding is an experience is desirable

• Prefrontal cortex coordinates all the information and determines behavior of individual

• Pathway:

  • Triggering stimuli

    • Natural rewards activate the pathways

    • sensory inputs are processed in the brain

  • Dopamine release

    • VTA releases dopamine

    • Dopamine travels to the nucleus accumbens and prefrontal cortex

  • Reinforcement of behaviour

    • Nucleus accumbens processes the reward signal- pleasurable feeling

    • Reinforces behaviors that lead to reward- increasing likelihood to repeat

  • Cognitive and emotional integration

    • Prefrontal cortex assesses the value of the reward and its implications for future behavior 

    • The amygdala and hippocampus help attach emotional significance and memory to the reward experience. 

PNS divisions

• Afferent neurons: transmit signals to CNS

• Efferent neurons: transmit signals from CNS

  • Somatic system

    • Voluntary

    • Conscious body movements

    • Motor neurons

    • Efferent signals from CNS to skeletal muscles 

  • Autonomic system

    • Refers to collections of motor neurons (ganglia)

    • In head, neck, thorax, abdomen, pelvis

    • Axonal connections of these neurons

    • Involuntary movements:

      • Controls visceral functions 

      • Heart rate

      • Digestion 

      • Respiration rate

    • Some actions work in tandem with the conscious mind

      • Sympathetic system

        • Utilized situations involving stress, strenuous physical activity, danger, excitement 

        • Fight or flight response

        • Increases force and rate of heartbeat

        • Increased blood pressure constricts blood vessels, dilates bronchioles

        • Suppresses digestion

      • Parasympathetic system

        • Housekeeping functions- like digestion

        • Utilized during quiet, low stress times

        • Rest and digest

        • Nerves of parasympathetic division are located around the sympathetic nerves

Vagus nerve

• Cranial nerve 10

• Contributes to innervation of the viscera

• Conveys sensory information about the state of the body’s organs of the CNS

• Responsible for: 

  • Heart rate

  • GI peristalsis

  • Sweating

  • Muscle movements in mouth, speech and keeping the larynx open for breathing 

Spinal cord

• Carries impulses from the brain to PNS

• Sensory info to brain

• Motor info to periphery

Sensory regions in the brain

• Primary somatosensory area

  • Located in the parietal lobes of each hemisphere

  • Integrates information regarding touch, pressure, temp, pain

  • Causes tingling in related body parts on the opposite side of the body- if stimulated

• Primary motor area

  • Located anterior to the primary somatosensory area

  • Stimulation of portions of the primary motor area causes movements of specific body parts on opposite sides of the body

• Homunculus

  • Representation of correlation between areas of the body from which sensory information projects to areas in the primary somatic sensory cortex

  • Size is related to the various regions correlated to the number of sensory receptors in the corresponding part of the body

• Association areas- integration

  • Areas surrounding the sensory and motor areas

  • Function: 

    • Integrating information from the sensory areas

    • Formulate responses

    • Transmit the response to the motor cortex

• Association areas- language

  • Broca’s 

    • Expressing language

    • Coordination of lips, tongue, jaw 

    • Initiates the complex series of movements necessary for speech

    • Damage- speak few words which are poorly pronounced- comprehend written and spoken words

    • Broca’s aphasia- hesitant and distorted speech

  • Wernicke’s

    • Understanding and formulating coherent speech

    • Coordinates input from auditory and visual areas

    • Damage- can speak but words make no sense

    • Wernicke’s aphasia- fluent language with made up or unnecessary words with little or no meaning to speech, difficulty understanding other’s speech with unawareness of mistakes

  • Arcuate fasciculus is believed to connect wernicke’s and broca’s area

  • How does speech work?

    • AP from eye reach the primary visual cortex- word is seen here

    • Word is recognized in visual association area

    • Word is understood in parts of Wernicke’s area

    • APs representing the word are conducted through association fibers that connect the wernicke’s to broca’s

    • Word is formulated in Broca's area

    • APs are conducted to the premotor area where movements are programmed

    • Movements are triggered in primary motor cortex

• Association areas- memory

  • Storage and retrieval of sensory or motor experiences

  • Short term memory: depends on transient changes in neurons, such as changes in membrane potential and reversible changes in ion transport

  • Long term memory: storage of memories for days and years

    • Permanent biochemical, molecular or structural changes that establish signal pathways that cannot be easily terminates

  • Long term potentiation: caused by a short burst of repetitive firing in the presynaptic neurons such that when there is single AP later, it will evoke a greatly enhanced response in the post synaptic cells

    • Effects last in relation to the number and intensity of repetitive firing

    • Occurs when a presynaptic cell fires at a time when the post synaptic membrane is strongly depolarized due to recent repetitive firing of the same presynaptic cell or other means

    • Late LTP:

      • Permanent alterations: 

        • Number and area of synaptic connections

        • Number and branching of dendrites

        • In gene transcription

        • Protein synthesis

      • Pathway

        • Repeated stimulation of presynaptic cell reaches a threshold such that dopamine, a modulatory neurotransmitter is released

        • Dopamine acts on GPCR that is coupled to adenyl cyclase

        • Increases level of cAMP

        • Activates protein kinase

        • Activates CREB which is a transcription factor

        • Turns on genes that make proteins involved in generating new synaptic connections

• Association areas- learning

  • Involves a change in the response to a stimulus based on information or experiences stored in memory

    • Store a memory

    • When a stimulus is encountered, scan your memories

    • Modify your response according, this means you learn

Consciousness

• EEG- recording of electrical activity along the scalp produced by the firing of neurons within the brain

• Sleep is semi conscious