spinal cord and reflexes and brain, exam #4

Spinal meninges:

• Specialized membranes

• Functions of the spinal meninges include:

  • Isolate spinal cord from surroundings

  • Carry blood supply

  • Continuous with cranial meninges

Meningitis:

Viral or bacterial infection of meninges

Three meningeal layers:

1. Dura mater

2. Archnoid mater

3. Pia mater

First Meningal layer: DURA MATER

• Outer most layer

• Touch collagen fibers

• Epidural space

The epidural space of the dura mater

• Between spinal dura mater and vertebrae

• Loose connective tissue and adipose tissue

• Anestheric injection site

Second meningeal layer: ARACHNOID MATER

• Middle menigeal layer

• Simple squamous epithelia

• Subarachnoid space

Subarachnoid space of the arachnoid mater

• Between the arachnoid mater and pia mater 

• collagen/elastin fiber network

• Filled with cerebrospinal fluid (CSF), which carries dissolved gasses, nutrients, and wastes

  • Shock absorber

  • Spinal tap (lumbrar puncture) withdraws CSF

Third meningal layer: PIA MATER

• Inner menigeal layer

• Mesh of collagen and elastic fibers 

• Bound to neural tissue

Spinal cord: ROOTS

• Branches of spinal nerves attached to cord

1. Posterior root

2. Anterior root

• Along posterior root is the posterior root ganglia, which are cell bodies of sensory neurons

Posterior root

Axons of sensory neurons

Anterior root

Axons of motor neurons

The spinal nerve:

• Posterior and anterior roots join on each side of spine

• Classified as mixed nerves

  • Carry both afferent (sensory) and efferent (motor) fibers 

Spinal reflexes are…

• Rapid automatic nerve responses triggered by specific stimuli

  • Controlled by spinal cord alone

  • Rapid response to preserve homeostasis

Reflex arc

• Wiring of a single reflex

• Begin at receptor, ending at effector

  • May or may not have interneurons

  • Tries to remove original stimulus (negative feedback)

Steps of a reflex arc:

1. Stimulation of a receptor

2. Activation of a sensory neuron

3. Information processing in the CNS

4. Activation of a motor neuron

5. Response of a peripheral effector 

Reflex classifications, Development

• Innate: developmentally or genetically programmed

• Acquired: learned

Reflex classifications: TYPE OF RESPONSE

• somatic : involuntary control of skeletal muscle

• Visceral: smooth muscle, cardiac muscle, glands, adipose tissue

Reflex classifications: COMPLEX OF CIRCUIT

• Monosynaptic: single synapse between sensory and motor neurons in CNS

• Polysynaptic: one or more interneuron

Reflex classifications: SITE OF PROECESSING

• Brain

• Spinal cord

Stretch reflex

• Monosynaptic

• Regulates muscle length, ex: knee-jerk response 

The largest part of the brain that processes somatic sensory and motor information:

cerebrum

Cerebrum functions:

• controls all conscious thoughts and intellectual functions 

• Memory storage and processing 

• Conscious and subconsiuous regulation of skeletal muscle contractions

The cerebrum association areas:

• Interpret incoming sensory information

• Coordinate motor response

The cerebrum integrative centers:

• Receive information from association areas

• Direct complex motor and analytical activities

Second largest part of the brain:

cerebellum

Cerebellum function:

• Adjusts postural muscles

• Fine-tunes conscious and subconscious movements

• Coordinates complex somatic motor patters

• Adjusts output of other somatic motor centers in brain and spinal cord

Diencephalon location:

• Under the cerebrum and cerebellum 

• Links cerebrum with brain stem

  • Has thalamus, which relay and processes centers for sensory info

  • Has hypothalamus, centers controlling emotions, autonomic functions, and hormone production

Diencephalon function:

• Processes sensory information 

• Emotion

Brain stem does what:

Processes information between spinal cord and cerebrum or cerebellum

The three regions of the brain stem:

1. Midbrain 

2. Pons

3. Medulla oblongata

Midbrain, also called mesencephalon:

• Processes sight, sound, and associated reflexes

• Processes visual and auditory date

• Generation of reflexive somatic motor responses

• Maintenance of consciousness

Pons:

• Somatic and visceral motor control

• Relays sensory information to cerebellum and thalamus

• Subconscious somatic and visceral motor centers 

• Connects cerebellum to brain stem

Medulla oblongata:

• Relays information

• Regulates autonomic functions

  • Heart rate, blood pressure, and digestion

• Connects brain to spinal cord

Physical protection of the brain

• Bones of the cranium

• Cranial meninges

  • Dura mater

  • Arachnoid mater

  • Pia mater

cranial meninges, Dura mater

• Inner fibrous layer (meningeal layer)

• Outer fibrous layer (periosteal layer)

• Layers often fused, but sometimes separate to create dual sinuses

  • Drains blood and cerebrospinal fluid (CSF)

craninal meninges, Arachnoid mater

• Subarachnoid space, contains CSF

cranial meninges, Pia mater:

Attached to brain surface

Cerebrospinal fluid (CSF):

• Supports brain weight

• Cushions brain

• Transports nutrients, wastes, chemicals, etc

Brain support and protection:

• Brain ventricles

• Dural folds

• Blood-brain barrier

Brain ventricles:

Connected cavities in brain with CSF

Dural folds:

• Folded layer of dura mater that extend into cranial cavity

• Stabilize and support brain

• Contain collecting veins (dural sinuses), removes waste

Blood brain barrier (biochemical isolation):

• Isolates CNS from general circulation

• Formed by endothelial cells of capillaries and astrocytes

• Lipids soluble compounds (O2 and CO2) diffuse in

• Water soluble compounds, proteins regulated